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Rough Idle

Joined
27 July 2009
Messages
425
Location
East Greenwich, RI, USA
My new, to me, NSX has a slightly rough idle and a bit of a stumble at initial throttle tip in. This make clutch engagement a little hit or miss. The car has 57,000 miles. Does this sound like a dirty throttle body or something else? If so, how do I clean the throttle body? Is it simply a case of spraying carburetor cleaner into the intake or is disassembly required? Any help would be appreciated.

Gary
 
Is there also a hesitation and stumble during acceleration at times?

If so, I’d start by checking the coil packs. Sometimes water gets into the space and corrodes them and can cause the same symptoms. It’s also the easiest thing to check first.
 
Acceleration appears to be fine. It's just at idle or slightly above. I will check the coil packs, anyway.
Thanks,
Gary
 
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Most of what you describe seems to be normal, perhaps associated with the NSX's 90 deg cylinder arrangement which create an uneven firing pattern on a 6 cylinder engine. The c30/32 has offsets on the crank to try and help; but, its not a perfect fix. The noise and vibration is most noticeable when in the cabin at idle. Get out and open the engine compartment and there is no noticeable vibration in the engine which is typically what you would get if you have an ignition misfire.

On my 2000, the vibration is most noticeable when the engine has not warmed up; but, has come off the fast idle associated with the operation of the air injection pump. I suspect that any engine vibration is transmitted to the cabin through the front engine mount which is why it seems worse inside the car than outside. On my car the vibration is more noticeable when things are cold. This may be due to improvement in operation of the engine; but, I also hypothesize that the front engine mount (and the others) may be warming up and becoming slightly more flexible which reduces the transmission of vibration to the cabin. On my car, the vibration is definitely more noticeable when its cold outside. If the front engine mount has partially failed that can result in much more direct contact between the engine and the cabin and that will definitely result in much more vibration (and noise). If your car was tracked or exposed to a lot of high engine temperatures this can lead to earlier failure of any of the engine mounts.

Contamination of the ignition coil 'noses' can lead to ignition misfires. However, true ignition misfires usually get worse as the engine load increases and they generally won't go away when the engine warms up unless the misfire was caused by moisture on the coil nose which evaporates when hot. If you can do the work yourself, you can check the coil noses for flashovers for free; however, having just gone through the spark plug replacement process I would not describe it as super easy. If you are going to pull the coils you might as well replace the sparkplugs while you are in there unless you know that they are relatively new. If the coil shows any signs of flashover on the nose then you absolutely should replace the matching sparkplug. If you do have a bad coil and need to replace it, be aware that Honda has this bizarre pricing thing where you can get either 3 or all 6 coils for the price close to a single coil. You just need to know the part number for this 'coil kit' and you can find it on Prime if you search for a bit.

If your 2002 is new to you, I will comment that the throttle tip in with the DBW can be fairly quick and the clutch engagement with the dual mass flywheel can be fairly quick (and a bit high). Having driven Euro cars for years with more forgiving clutches / throttles this made for a lot of lurch, stall, rev like crazy when I first got the car.

The DBW 2002 does not have a separate idle air control valve. On the pre DBW cars when this gets grotty idle control can become a problem. The DBW cars do idle speed control directly off of the throttle plate so that is not a problem. The exception to this is the base idle speed. If you were having a problem with low idle then you might have a contamination problem. A dirty throttle plate may look offensive; but, really has minimal effect other than perhaps slightly messing with air flow when you are pedal to the metal. Cleaning by spraying into the throttle opening may clean the front side of the plate so that it looks nice - much harder to get at the back side and doesn't deal with the air passages. If you have throttle body related problems its more likely to be in all the little air bleed passages around the periphery of the throttle plate. You might be ale to do the spray can straw into the passages thing; but, reality is the throttle body probably needs to come off to do it correctly. If the car has always had the OEM style dry pleated air filter and is not turbo or supercharged I would be less inclined to be concerned about the throttle body. If the car has or ever had an oiled filter element then I would be inclined to check the throttle body because a lot of oiled filter element owners fall into the more oil is better category which can result in oil contamination of the throttle plate and the air passages. If your car has significant blow by or the PCV system or EGR system has issues this can also result in more contamination on the throttle body because of more undesirable stuff floating around in the intake manifold.
 
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Hi OldGuy,
Thank you for all the detailed information. I had a 2003 NSX that did not feel like this at all. It is particularly noticeable when one blips the throttle at idle. The engine hesitates significantly then revs up. This is what sounds bad and makes clutch engagement so iffy. At fast idle, the roughness is quite noticeable.
Thanks,
Gary
 
Is the rough idle engine vibration (which could be a slight ignition misfire) or is the idle speed fluctuating? As noted, misfires usually get worse with engine load. If the idle speed is fluctuating that could be a fuel mixture problem, perhaps running a bit lean. Lots of potential causes; but, if it was really bad you would normally get a fuel mix error code. Have you checked for any stored codes in the ECU? Once the engine temp has increased a bit and the engine is off fast idle it goes into closed loop operation running off of the O2 sensors. Based upon what others have reported it seems as if it is possible for the O2 sensors to be off; but, not off 'enough' to cause an error code. This could be causing the engine to run a little lean with driveability problems. If you have an OBDII code reader that can display the fuel trims and if they are in large single or double digits that might be an indication that the O2 sensor is off or you have a fuel delivery problem someplace else.

A fuel problem can also cause a stumble just on initial application of the throttle. ECUs typically use the throttle position sensor to indicate that the throttle is opening and apply a little extra fuel enrichment (the equivalent of the accelerator pump on a carb). If your sensor has a worn spot on it, that might be screwing up the initial opening signal. If the sensor was quite out of spec that would normally cause an error code. The service manual has a procedure for checking the TPS. The TPS voltage ranges (which trigger error codes) can test in-limit even if it has a slight worn spot. The more important test would be to check the wiper voltage and make sure that it increases smoothly as the throttle opens. As an observation the TPS tends to be pretty dumb-ass reliable and given the mileage on your car it would seem unusual to suffer a TPS failure. Note that a TPS problem would typically not cause engine vibration or rough idle.

The DBW system might be having a little glitch on initial opening; but, that is a completely different kettle of fish. As an observation, I don't ever recall seeing a report of a problem with the DBW system on Prime so I probably would not go looking there except as an absolute last resort.
 
Hi OldGuy,
The idle speed is not fluctuating. You have given me many great ideas to try. I do have an OBDII reader and will test for stored codes (great idea). The car is in the shop for other things at the moment, but should be back home for the end of the week. I will perform the tests you suggested and get back to Prime. Thank you very much. You are a terrific resource.
All the best,
Gary
 
OK, now that I have the car back, I have some more (or better) information. The symptoms seem to get worse as the RPM increases. It seems the worst at about 2000 RPM. After that it's hard to tell as the vibration is smoothed out just due to the higher frequency of the vibration. It sure feels like a misfire to me. I don't have the most sophisticated OBDII reader, but it shows no codes. Should I be pulling out the coil packs? How hard are they to get out? I'm pretty handy with a wrench. They sure don't look particularly easy to get at. I assume I attack them from the top. Am I looking for tracking on the noise of the coils?

Thanks,
Gary
 
The coil packs are very easy to remove. Just make sure when you put the covers back on that they are aligned properly with the gasket so water doesn't get into them easily. It's usually the back bank of coil packs that go bad due to water draining onto them from the vent behind the glass hatch.
 
Great! Thank you DocL. Is it likely that I can just clean the corrosion / tracking on the nose of the coil, or is replacement likely / necessary? How do I find the part number for the group price on coils. It doesn't show up at Delray Acura's parts list.
Gary
 
First pull them and see what they look like. You can give them a good cleaning, but it is probably best to order new ones if they are rusted. I haven't looked for parts in a long time, so just doing a Google search is probably your best option. Before you remove the plugs take a rag and clean out the channels. I removed a bunch of grime that would have fallen into the cylinders.
 
new set of 6 coils and 6 spark plugs $125. 1hr install, easy DIY.
throttle body removal and cleaning, $5 can of throttle body spray, a rag and a old toothbrush. 1.5hr DIY, simple disassembly of airbox and a unplugging a few hoses/connectors.

this is 2 beer job.

3fhQlCZD6-R-AToi54qzmFYa-oCzb25ly-H1a5GWLj8KVJ_9HC56B-a25TK4m-7iTa9cZoPi4LcPoWCkxUoMY8b6xHvgbSOjIKhCvsSPnJTjjI6gleg4dgZb1E_5Ll2tr17UQoe--_qZkiQWF5GaFo09C1IY6QuFps3cxGRb9BOivBpekx25cQvCiz3vLnQjDjol4T-UVNgmc88pJsrHh4cNCPxljocfGAUBx47ou4iKyz2RTlTulVqZQm252MudpIsT8V7STP_zQHlCBJ_1t3rBmkOi0X49bIWmYCdComwJPn4WMwnnkVV1OX_uMRvm7yUk0hJQth6l98cHDRDDivtH4ADfiOAPtTpZIvOjKPYbw9-_elEmaGsDZxOLla3RxwMA5cAtWTTTpKgWOkJdHCDk7Mi2UsD2J2t_qQDqLktga47efRftDcmT_Ny3EfDv7En94yst6vyN4VnnRaacI3nrAtwJOcPIaRF58R0sb1JH9ME0kzr-P-m2l_n22lkkDbFE4LnM_zeQ8YNgl8YVgRlMV9RaI-RXx8CwR9UoNzkD-wBxuJA-RDX0MbvaLn1obcYlqzPDHh-8BDn9_vmzGdy7hC3iyq9o9f9O9WD1JayPJbYQVDXXbn6WsXmmonr4S71LVwEPew02O_Z1PpuyH7Tkz8CW7GXv-UaXraVUEiRQ3q9iydaFLyN8OPXuTgSoJHeSLrgw_AwDIoqjy_BreXq7=w1560-h1170-no
 
Great! Thank you DocL. Is it likely that I can just clean the corrosion / tracking on the nose of the coil, or is replacement likely / necessary? How do I find the part number for the group price on coils. It doesn't show up at Delray Acura's parts list.
Gary

Agree with DocL- if you see significant rust, probably better to replace. The main culprit for damage is if the sheet metal is lifting away from the plastic housing. Here is a picture from Kaz's blog that shows it in a really bad coil:

http://www.nsxcb.co.uk/entry.php?2505-Eng-Refresh-Health-Check-etc-04

For domestic parts orders, I have always used Tim Poliniak at Acura of Peoria. You get free shipping plus about 30% off list price if you are a NSXCA member.

www.oemacuraparts.com
 
Wow! What a mess! I had a PPI done a couple of weeks ago where he did a compression check. Obviously, he had to pull the coils to do that. If they were really bad, I would have thought he would have seen / said something. Wouldn't a misfire like that show up on the OBDII. I am showing no codes.

Thanks,
Gary

Agree with DocL- if you see significant rust, probably better to replace. The main culprit for damage is if the sheet metal is lifting away from the plastic housing. Here is a picture from Kaz's blog that shows it in a really bad coil:

http://www.nsxcb.co.uk/entry.php?2505-Eng-Refresh-Health-Check-etc-04

For domestic parts orders, I have always used Tim Poliniak at Acura of Peoria. You get free shipping plus about 30% off list price if you are a NSXCA member.

www.oemacuraparts.com
 
Cool! Where do I get 6 coils and 6 plugs for $125? Part number?
Thanks,
Gary

i dont have the part # for the spark plugs as i have a 3.0 1995

but the coils are the same.
[h=1]06300-PR7-305[/h]
 
Since you have now determined that the engine roughness does not go away at higher engine loads, then it very well could be a misfire and removal of the coils for inspection would be a good first place to look.

The individual coils have a bare metal pad which the mounting bolts bear against. This surface can incur surface rusting if any moisture has made its way past the coil covers. I would not be concerned about mild surface rusting if you can clean it up with a 3M abrasive pad or some 300 grit SiC paper. Serious rust may not be a problem; but, may be an indicator that there are more serious problems elsewhere.

The critical area that you want to check is the long nose of the ignition coil that fits over the spark plug terminal. On the end of the nose there is a rubber boot that fits over the sparkplug. If misfires due to flashovers have occurred this is where evidence will first show up along with traces on the surface of the sparkplug porcelain. You can search the web using the term 'carbon tracking on ignition coil' and you will get a number of hits describing the problem. This site has a photo that is probably as good as any:

https://easyautodiagnostics.com/chrysler/2.0L-2.4L/carbon-tracks-misfire-3

The inside surface of the rubber boot on the coil nose and the spark plug porcelain should be nice and clean with no tracking of any kind. The nose above the rubber boot should not have any tracking of any kind. If you do have tracking on that hard part of the nose the coil has to go because tracking there is a sign of serious coil problems. For tracking on just the rubber boot, in a pinch, you could try cleaning it with 99% IPA or a zero residue electrical contact cleaner. However, tracking can cause surface damage and cleaning cannot fix that. Any tracking on the coil nose or that rubber boot and the matching sparkplug has to go.

The ignition coil has a rubber gasket on its base where it contacts the spark plug well which should prevent 'stuff' from entering into the spark plug well. If you have signs of water contamination on the nose of the coil it is an indication that the coil base gasket is not sealing. I don't recall seeing the base gasket listed as a separate part so you should plan for replacement of the coil if the base gasket is compromised. When I did my sparkplugs I greased the base gasket liberally with silicon dielectric grease to help insure a good seal. With grease on the gasket it becomes a near air tight seal. When I push the coil into the well the coil tend to pop back out because of the pressurization of the air in the well. That spark plug well should never be getting stuff in it. When replacing the spark plugs or the coil, also grease the spark plug insulator and the inside of that rubber boot. If moisture ever gets into the spark plug well this helps to seal the nose reducing the chances of tracking along the spark plug insulator. Greasing the boot and the plug will also make removal easier in 7 years. Sometimes the rubber boot can bond to the insulator surface making removal harder.

I believe this is the part # for the 6 pack coil kit:

06300-PR7-305

You can search on the web using the part number and you should be able to find the kit from authorized Acura parts vendors for less than $110. Be aware that at one time the kit also included sparkplugs. However, the sparkplugs were the heat range for the C30, not the C32. If you order the kit and by some odd freak of circumstance it has the sparkplugs included with it, don't automatically use the plugs without checking to confirm they are the right heat range.

Since you have a T roof car, I suggest making arrangements to prop up the engine cover and remove the 3 point brace in the engine compartment. You can remove the coil covers and the coils with the brace in place; but, it is a real hassle. You can also R&R the sparkplugs with the brace in place; but, it is a triple hassle and it is very hard to properly torque the plugs with a click type wrench with the brace in place.

When you put the coil covers back on, the coil covers are marked on the inside of the cover to indicate front and rear. The rubber gasket should go along the top edge of the coil cover. No gasket on the bottom edge. When re installing the cover grease the gasket with a little silicon dielectric grease to help it slide into position without coming off the cover.

Your OBDII coils have a 3 pin plug on them and it has a weather tight seal so contamination should not be a problem. Also, voltages are relatively low so you won't be getting flashover here. When removing the coils this plug has a retaining clip which must be pressed to pull the plug out of the coil (you are doing this blind). Even with the clip released the plugs can be a real b**** to get out of the coil because the plug has a little rubber lip seal which likes to stick to the housing. I also lube the plug and its little rubber lip seal with dielectric grease to make removal easier in the future.
<!-- DO NOT change linkToTagId="rwid" as the catalog response has this ID set -->
 
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You guys are all amazing! I recognize most of you from my previous days on Prime (4 years ago)l You've been such an incredible help (as usual). I plan to pull the coils on Monday and will keep you all up to date on my progress. I, also, am a big fan of dielectric grease and will be using it liberally in the reassembly. I especially appreciated the detailed disassembly instructions. I had a 2003 NSX before that was totaled by DWI driver, so I have a lot of experience working on my old NSX but never had to do the coil thing. Will be back shortly.
Gary

Since you have now determined that the engine roughness does not go away at higher engine loads, then it very well could be a misfire and removal of the coils for inspection would be a good first place to look.

The individual coils have a bare metal pad which the mounting bolts bear against. This surface can incur surface rusting if any moisture has made its way past the coil covers. I would not be concerned about mild surface rusting if you can clean it up with a 3M abrasive pad or some 300 grit SiC paper. Serious rust may not be a problem; but, may be an indicator that there are more serious problems elsewhere.

The critical area that you want to check is the long nose of the ignition coil that fits over the spark plug terminal. On the end of the nose there is a rubber boot that fits over the sparkplug. If misfires due to flashovers have occurred this is where evidence will first show up along with traces on the surface of the sparkplug porcelain. You can search the web using the term 'carbon tracking on ignition coil' and you will get a number of hits describing the problem. This site has a photo that is probably as good as any:

https://easyautodiagnostics.com/chrysler/2.0L-2.4L/carbon-tracks-misfire-3

The inside surface of the rubber boot on the coil nose and the spark plug porcelain should be nice and clean with no tracking of any kind. The nose above the rubber boot should not have any tracking of any kind. If you do have tracking on that hard part of the nose the coil has to go because tracking there is a sign of serious coil problems. For tracking on just the rubber boot, in a pinch, you could try cleaning it with 99% IPA or a zero residue electrical contact cleaner. However, tracking can cause surface damage and cleaning cannot fix that. Any tracking on the coil nose or that rubber boot and the matching sparkplug has to go.

The ignition coil has a rubber gasket on its base where it contacts the spark plug well which should prevent 'stuff' from entering into the spark plug well. If you have signs of water contamination on the nose of the coil it is an indication that the coil base gasket is not sealing. I don't recall seeing the base gasket listed as a separate part so you should plan for replacement of the coil if the base gasket is compromised. When I did my sparkplugs I greased the base gasket liberally with silicon dielectric grease to help insure a good seal. With grease on the gasket it becomes a near air tight seal. When I push the coil into the well the coil tend to pop back out because of the pressurization of the air in the well. That spark plug well should never be getting stuff in it. When replacing the spark plugs or the coil, also grease the spark plug insulator and the inside of that rubber boot. If moisture ever gets into the spark plug well this helps to seal the nose reducing the chances of tracking along the spark plug insulator. Greasing the boot and the plug will also make removal easier in 7 years. Sometimes the rubber boot can bond to the insulator surface making removal harder.

I believe this is the part # for the 6 pack coil kit:

06300-PR7-305

You can search on the web using the part number and you should be able to find the kit from authorized Acura parts vendors for less than $110. Be aware that at one time the kit also included sparkplugs. However, the sparkplugs were the heat range for the C30, not the C32. If you order the kit and by some odd freak of circumstance it has the sparkplugs included with it, don't automatically use the plugs without checking to confirm they are the right heat range.

Since you have a T roof car, I suggest making arrangements to prop up the engine cover and remove the 3 point brace in the engine compartment. You can remove the coil covers and the coils with the brace in place; but, it is a real hassle. You can also R&R the sparkplugs with the brace in place; but, it is a triple hassle and it is very hard to properly torque the plugs with a click type wrench with the brace in place.

When you put the coil covers back on, the coil covers are marked on the inside of the cover to indicate front and rear. The rubber gasket should go along the top edge of the coil cover. No gasket on the bottom edge. When re installing the cover grease the gasket with a little silicon dielectric grease to help it slide into position without coming off the cover.

Your OBDII coils have a 3 pin plug on them and it has a weather tight seal so contamination should not be a problem. Also, voltages are relatively low so you won't be getting flashover here. When removing the coils this plug has a retaining clip which must be pressed to pull the plug out of the coil (you are doing this blind). Even with the clip released the plugs can be a real b**** to get out of the coil because the plug has a little rubber lip seal which likes to stick to the housing. I also lube the plug and its little rubber lip seal with dielectric grease to make removal easier in the future.
<!-- DO NOT change linkToTagId="rwid" as the catalog response has this ID set -->
 
When I hear about rough idle, I would first advise to disconnect the primary O2 sensors. It will throw a CEL. But if the rough idle disapear, you can link it to O2 sensors. Before spending $ in coil packs.

And for throttle body cleaning, I am a bit afraid of spraying any cleaning solution in it as there are screws on the VVIS that are glued. Don't know if this can be a cause of loosening screws there.
 
Great idea, Asylum! I will try that.

Monday morning follow up. I pulled the coils and plugs. They all look brand new, like they just came out of the box. There is no sign of corrosion anywhere. I, also, checked the primary resistance on all the coils and all were in spec. Dead end? Perhaps, not. I appear to have the wrong spark plugs. The shop manual and Acura of Peoria, both recommend NGK PFR6L-11 plugs. I have NGK BKR6EIX-11. Can that cause the problem?

Thanks to all,
Gary

When I hear about rough idle, I would first advise to disconnect the primary O2 sensors. It will throw a CEL. But if the rough idle disapear, you can link it to O2 sensors. Before spending $ in coil packs.

And for throttle body cleaning, I am a bit afraid of spraying any cleaning solution in it as there are screws on the VVIS that are glued. Don't know if this can be a cause of loosening screws there.
 
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Sorry to break it to you; but, those spark-plugs should be just fine. They are a newer design iridium plug rather than the original double platinum PFR6L-11 plugs. The plugs are the same dimension and heat range as the PFR6L-11. I had the BKR6EIX-11 plugs in my NSX from 2010 until this year and just switched them out. They came out looking just fine. Normally, double platinum plugs are in the $4-6 range (Cdn $) and the iridium are in the $6+ range from places like Rock Auto. However, the only listed application for the PFR6L-11 platinum is the NSX so I think it gets the special NSX tax which puts them up around $12 a pop (even more from the dealer). Whoever last changed the plugs decided to save $36 and install a newer design plug to boot.

However, if those plugs were just recently installed and the problem emerged recently after the install, then the plugs might be the problem. There have been issues with counterfeit Denso and NGK plugs. A search on 'counterfeit ngk iridium' will get you a number of hits.

http://www.ngk-sparkplugs.jp/english/techinfo/fake/index.html

Fake iridium plugs suffer from rapid electrode wear (amongst other issues) so if a gap check shows excessive gap you might have some fakes. If the sparkplugs have been in the engine for a while and the rough idle emerged recently then fake plugs are unlikely the problem. If you know that the spark plugs came from some place like Rock Auto or a trusted vendor they are unlikely fakes. If they were acquired from an eBay or Amazon vendor, then they might be up for scrutiny.

The reality is I suspect that you will need to start looking elsewhere. Absent a scanner which can let you look at the actual O2 sensor output and the fuel trims, the disconnect the O2 sensor may be your next no cost effort; but, make sure it is the primary sensors that you disconnect and remember that you have front and back primary sensors so you may need to do a front only, back only, both test. Disconnecting the secondary O2 sensor will do nothing other than generate an error code.

As an observation, when narrow band O2 sensors start to fail they commonly start to output a low voltage which the ECU interprets as running lean. The ECU increases the fuel pulse width in response which causes the engine to run richer. If its not really bad it may not trigger a mix out of range error code; but, gas mileage will suffer. Driveability usually does not suffer under rich operating conditions unless it gets to the point that the ECU generates a mixture out of range error. If the O2 sensor were driving the ECU to reduce the fuel pulse width that causes the engine to run lean and it doesn't take too much to the lean side to start causing driveability issues. I think that kind of error from an O2 sensor is not common. However, if you don't know when your fuel filter was last changed a dirty fuel filter can result in low fuel pressure and that can cause the same kind of lean driveability issues.
 
Well, today is O2 sensor day. Can I assume the Primary O2 sensors are the ones stuck in the exhaust manifold and the secondaries are stuck in the cats?

Gary

Sorry to break it to you; but, those spark-plugs should be just fine. They are a newer design iridium plug rather than the original double platinum PFR6L-11 plugs. The plugs are the same dimension and heat range as the PFR6L-11. I had the BKR6EIX-11 plugs in my NSX from 2010 until this year and just switched them out. They came out looking just fine. Normally, double platinum plugs are in the $4-6 range (Cdn $) and the iridium are in the $6+ range from places like Rock Auto. However, the only listed application for the PFR6L-11 platinum is the NSX so I think it gets the special NSX tax which puts them up around $12 a pop (even more from the dealer). Whoever last changed the plugs decided to save $36 and install a newer design plug to boot.

However, if those plugs were just recently installed and the problem emerged recently after the install, then the plugs might be the problem. There have been issues with counterfeit Denso and NGK plugs. A search on 'counterfeit ngk iridium' will get you a number of hits.

http://www.ngk-sparkplugs.jp/english/techinfo/fake/index.html

Fake iridium plugs suffer from rapid electrode wear (amongst other issues) so if a gap check shows excessive gap you might have some fakes. If the sparkplugs have been in the engine for a while and the rough idle emerged recently then fake plugs are unlikely the problem. If you know that the spark plugs came from some place like Rock Auto or a trusted vendor they are unlikely fakes. If they were acquired from an eBay or Amazon vendor, then they might be up for scrutiny.

The reality is I suspect that you will need to start looking elsewhere. Absent a scanner which can let you look at the actual O2 sensor output and the fuel trims, the disconnect the O2 sensor may be your next no cost effort; but, make sure it is the primary sensors that you disconnect and remember that you have front and back primary sensors so you may need to do a front only, back only, both test. Disconnecting the secondary O2 sensor will do nothing other than generate an error code.

As an observation, when narrow band O2 sensors start to fail they commonly start to output a low voltage which the ECU interprets as running lean. The ECU increases the fuel pulse width in response which causes the engine to run richer. If its not really bad it may not trigger a mix out of range error code; but, gas mileage will suffer. Driveability usually does not suffer under rich operating conditions unless it gets to the point that the ECU generates a mixture out of range error. If the O2 sensor were driving the ECU to reduce the fuel pulse width that causes the engine to run lean and it doesn't take too much to the lean side to start causing driveability issues. I think that kind of error from an O2 sensor is not common. However, if you don't know when your fuel filter was last changed a dirty fuel filter can result in low fuel pressure and that can cause the same kind of lean driveability issues.
 
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