Fluctuating idle

[lithiumus]

It may be something simple... but my car wont stay at a steady idle. After the car warms up, the idle drops low (almost 500) then the idle control automatically raises the idle but usually too high (1,100) then the idle drops again to almost 500. The goes on and on when i'm idling. The car drive fine and I recently had a 60k tune up at Autowave. I mentioned rough idle but everything seemed to check out fine.

Is my idle just set too low and maybe raising it a little would fix it or could this be build-up somewhere? I drive it quite hard last month and that is when this started happening. Any help would be appreciated. Thanks in advance.

 

[V12NSX]

One reason for this is "gunk" in the throttle body. This causes the butterfly to stick and not be able to maintain a smooth idle. It's easy to fix - just undo the rubber "snorkel" from the air filter box and spray some carburetor cleaner on a shop rag and wipe out the inside of the metal throttle body all around the butterfly. Keep doing this till it's clean and that will probably take care of the problem.

S.L.

 

[Larry Bastanza]

This is a symptom of a vacuum leak. Check all you hoses to/from the throttle body, check the fuel pressure regulator vacuum line. You can CAREFULLY use a can of carb cleaner to spray around hoses to see of they might be leaking. Or maybe a little safer would be to spray some carb cleaner on a small paint brush and "paint" around by the hoses and see if you find a leak.

HTH,
LarryB

 

[hlweyl]

Had the same problem on other Honda's ended up being the Idle Air control valve. First check for vacuum leaks and clean throttle body as suggested first.

good luck

 

[lithiumus]

Thanks a bunch guys. I'm going to try this after lunch today. I'll let you know how it goes...

 

[NSX-Racer]

You may also watch this thread with about the same problem discussed.

 

[NSX_V]

i had the same problem, but it was idling at 1500-2000 up and down. i got acura to take a good look at it and i ended up ordering a EACV(electronic air control valve). they put it on and cleaned the throttle body. now it runs nice, smooth and stable. i hope this helps and good luck!

 

[lithiumus]

I finally cleaned the throttle body. Man, the cloth was black! It's pretty cold out here but I'll probably do another cleaning when it's warmer. It definitely fixed the problem but I think I have another issue...

I think one of my cats is dead. After the car warmed up, the smoke from the exhaust on the right tailpipe went away while the left tailpipe spewed smoke continuously and smelled terrible. What is an easy way to confirm this?

 

[hlweyl]

It could be the residual cleaner used to clean the throttle body, see if it burns off. Blue smoke out of the tailpipes is burning oil, sweet smelling thick white smoke is coolant. Hopefully you don't have a blown head gasket.

 

[lithiumus]

didn't burn off. Had the car running for over 20 mins. Smoke was white and nothing sweet about it! It basically smells the same as when I started the car up, yet the right tailpipe is clean and smokeless after about 5 mins.

 

[hlweyl]

Probably the best thing to do is have a leak down test done.

good luck

 

[lithiumus]

I failed the emissions test yesterday. I'm not certain that it's the cats but I got a pair of known good cats and swapped mine out. Going to get it smogged again tomorrow.

The test failed only when the vehicle was idling. At high idle / driving, it passed with flying colors. Leads me to believe it may be EACV or another leak somewhere causing my idle mixture to be too rich. I don't have constant fluctuating idle but it comes once in a while when I'm at a traffic light and it fluctuates ever so slightly approx. <100rpm variance. (sounds like it is proabably a leak somewhere)

If the smog fails again (ruling out the Catalytic convertors), I'm going to get the leak down test done to find the leak, etc.. Thanks again for all your advice everyone.

 

[lithiumus]

It's been more than a year but I realized that I never posted the final results of this...

http://www.nsxprime.com/forums/showthread.php?t=54229

This should also help people who are searching...

In my case, it was a dripping fuel injector. Probably a rare case, but something to add to the root cause database!

 

[nsxtasy]

I just experienced the same problem. In my case, the idle was fluctuating between 1500 and 2500 RPM. We tried spraying carb choke cleaner on the throttle body and idle control valve, but it didn't help. So this morning we replaced the idle control valve (not cheap, almost $400). Problem solved. Thanks to Nabil at First Class Automotive in Orlando.

 

[Geo05nsx]

Ok bringing back a very old thread. I have a 2005 NSX. I'm experiencing the exact problem as the OP stated, but it's only happening during idle in neutral. If I push down on the clutch pedal and disengage it, the idle will normalize. I'm running SOS 350 clutch with their lightened flywheel and the problem appeared after the clutch/flywheel was installed. The car drives fine, was checked for leaks (none), no CEL, dealer reset the ICV but said the car didn't "relearn" the idle.

Has anyone else had problems running the lightened flywheel? Could that cause the fluctuating issue? Would it be a poor clutch install problem? But the clutch has no issues while driving or shifting. Any thoughts? Thanks

 

[Old Guy]

Your 2002 does not have an idle control valve (idle speed control is done by the DBW control). Your comment

but it's only happening during idle in neutral. If I push down on the clutch pedal and disengage it, the idle will normalize.

is a bit confusing. You say the problem only happens during idle in neutral; but, if you push down the clutch and disengage it (which normalizes the idle), isn't that in neutral which is when you say the problem occurs? That said, the ECU on the later cars utilizes 3 signals to switch into idle control mode.
- brake switch
- clutch switch
- transmission neutral switch

Seems like your ECU might not be getting one of the signals. If the car does not go into idle until you shift into neutral, then there might be a problem with the clutch switch. That said, best to get the service manual and go through the test procedure for the Idle Control System set out in the Fuel section.

What did your dealer do when he reset the non existent ICV? There is a procedure on the later cars for setting the idle speed that involves the service check connector. However, if the idle control system is not getting activated because it is not getting the signals, the idle setting procedure won't fix that.

 

[Geo05nsx]

Old Guy thx for the reply. I know it's a bit confusing, so let me try to clarify. When the engine is on, and the shifter is in neutral, with feet off all pedals, the idle would fluctuate between 500-1000, exactly as the OP described in the first post. But when I push down on the clutch pedal all the way, the idle would settle down and stabilize to ~600 rpm, completely normal. Also, if the car is warmed up and I turn it off, then turn it right back on (clutch in, shifter in neutral), then let go the clutch pedal, the idle drops to 0 very quickly and car stalls -- it feels like the lightweight flywheel lost the inertia and the engine can't catch it fast enough. But if I keep the clutch pedal depressed, everything's ok and I can drive away and then everything normalizes.

As for the dealer "ICV"...that was my typo. Dealer's note said "idle air control re-learn didn't work. reset idel screw system still did not relearn. recommend iac valve inspection and flush coolant." Both were done later but problem persisted.

 

[Old Guy]

600 +/- 50 RPM is the initial target when adjusting idle speed in the idle set up procedure with the SCS shorted. Once the SCS short is removed and you raise the RPM to 1000 RPM briefly the idle speed is supposed to stabilize at 800 +/- 50 RPM as the final step in the procedure. So, your idle speed of 600 RPM while stable, is abnormally low. However, if you are estimating speed based upon your tach, your tach could also be out of calibration (a common problem). If you have access to an OBDII scanner (or scanner app and dongle), a good one should be able to display the engine RPM that the ECU is measuring and confirm whether the RPM is correct or incorrect.

The

recommend iac valve inspection and flush coolant." Both were done later but problem persisted.

action by the dealer is a bit of a mystery since there is no iac valve to inspect. That is a conversation that you may or may not want to have with the dealer.

If you confirm that your idle is stabilizing at 600 RPM, that is too low and will always create a problem for maintaining a smooth idle. However, I am going to speculate that if the ECU is not getting the correct signals from the brake switch, the clutch switch or the transmission neutral switch, it may not be possible to successfully take the ECU through the idle setting procedure. The service manual procedure does specify that the transmission must be in neutral when carrying out the procedure.

With the clutch engaged (pedal up) and transmission in neutral, the ECU needs the 'neutral' signal from the ECU to tell it to go into idle control mode. When you are in gear; but, stopped with the clutch pedal pressed to the floor the clutch switch gives a signal to the ECU to put it into idle control. So, just guessing that because the idle stabilizes with the clutch pedal pressed down, the ECU is getting the signal from the clutch pedal. When you let the clutch pedal up with the transmission in neutral the signal from the clutch pedal disappears; but, should be replaced by the signal from the transmission that the car is in neutral so it stays in idle control mode. If you let the clutch pedal up and there is no neutral signal from the transmission then the ECU assumes that the car is in gear, clutch is engaged and you should be pressing the gas to go forward - hence no idle control. So, based upon your symptoms my first guess would be that something is up with the neutral switch signal. You can test for the neutral switch signal using the procedure in the service manual. As an observation, since the transmission came off when the clutch was replaced, the neutral switch had to be disconnected. Its possible that they completely forgot to connect the neutral switch during the re installation, or that the plug is not completely inserted in the switch or that it got buggered up some how. So as a first step visually check the neutral switch. If it appears OK then the next step would be to check the signal, including the brake pedal and clutch pedal signals at the ECU as set out in the service manual.

The idle setting screw on top of the throttle body allows a small amount of air to by-pass the throttle plate and this is what sets the base idle speed of the engine. Air is admitted to this system by a port upstream of the throttle plate. It is possible that 'something' has gotten in there and is buggering up the air flow for the base idle setting. However, this port is upstream of the throttle plate and normally doesn't get exposed to products from the PCV and EGR systems so should stay clean, particularly if you are using the OEM paper air filter. You could give this port a shot with some throttle body cleaner using a straw in the port if you are inclined; but, I don't think it is the problem. Also, the dealer probably did this as part of their service attempt.

In summary, you could have two problems. Missing signal(s) to the ECU and a base idle that is too low. I think you need to check for the missing signals first before trying to set the idle speed.

A light flywheel does not help the problem; but, I would be extremely surprised if it is causing the radical idle problems you are describing.

 

[Geo05nsx]

Wow Old Guy that's a wealth of info there! Thank you and much appreciated! I will definitely look into the neutral switch. BTW, I checked the car again and I can tell you I misread the idle a bit, it's actually idle at 8-900 rpm, not 600. So when it's not fluctuating, the idle seems to be within your indicated range. However, I can always elicit the fluctuating idle if I depress the clutch pedal and then left it back up right away.

The other interesting thing is that if I disconnect the battery and reset the ECU, the first time I fire it up the idle goes absolutely nuts and can barely keep the car from stalling itself out. But with each successive start/stop, the idle settles down and the fluctuation lessens. It never goes away but at least it's manageable. It seems like the car learns it over time but never can get it 100% right.

 

[Old Guy]

I don't think the ECU has any flash memory. The idle setting procedure set out in the service manual may set values stored in keep alive memory. However, without seeing the source code its all speculation as to what the idle setting procedure is doing. When you reset the ECU, it wipes everything in keep alive memory which 'might' explain the weird idle behaviour when reconnecting the battery. However, my 2000 sits with the battery disconnected for about 6 months a year and when I reconnect the battery the car starts right up and idle speed and stability has never been an issue. According to the service manual, the SCS has to be shorted for the ECU to go into the idle learning mode. Presumably you don't have the SCS shorted so the ECU is not going through an idle learning / setting process when you do those restarts. I am guessing something else is happening.

Once the engine is up to operating temperature the ECU will start to correct the fuel trims and store those fuel trims in keep alive memory (called long term trim). If your car is requiring a lot of long term fuel trim (because it is running lean or rich on the fuel mix) and you erase those fuel trim values the engine may run poorly until such time as the fuel trims get re established which occurs with repeated operation of the engine. High fuel trims are a sign of problems (low fuel pressure, dirty injectors, leaky injectors ...........on and on). I don't think the fuel trims are the root cause of your idle weirdness; but, it might be contributing to the problem. If you have access to a scanner you should be able to read the fuel trims. In a perfect world the long term trims and short term trims would be low single digit numbers. If the engine is operating with high single digit or double digit numbers, then you have a fuel problem which may just be making your idle problem worse.

 

[Geo05nsx]

My car has just a downforce intake and SOS exhaust, engine wise everything else is bone stock. The car only has 20k on it. It's regularly maintained and has no driving hiccups besides this issue. I think like you said it's probably still the transmission signal issue since it began after the clutch/flywheel install. I also had an OS Giken LSD and 4.44 FD installed into the trans at the same time. The LSD is very aggressive but I don't think that would cause idle issue...haven't seen anyone on the forum with OSG report this problem. No EPS light with the LSD either.