• Protip: Profile posts are public! Use Conversations to message other members privately. Everyone can see the content of a profile post.

Vibration on idle

Rating - 0%
0   0   0
Joined
22 December 2020
Messages
7
Hi guys.

Just trying to iron out a few minor concerns with this 91 manual NSX.

I come for a slightly different Honda background- being s2000s and ITR’s but the NSX is all new to me. Incredible but struggling as I don’t know enough about them yet.

Recently it’s had a major service.

Hasn’t done much driving since the service but even before the service I noticed the car vibrates on idle.

I don’t think it’s normal because the moment you take off, as soon as u start rolling the slightest bit, it all goes away. And becomes smooth as.

I have read that people back off the front and rear engine mount, rev the car a few times and then re- torque the mounts- settles the motor in again.

Is this a good start?

Any input is greatly appreciated.

Cheers heaps!!!
 

goldNSX

NSX Prime Moderator
Rating - 0%
0   0   0
Joined
15 May 2004
Messages
6,899
I think your problem is not the engine mounts as it would vibrate alle the time.

One cause could be the fuel injectors after a long time not driving.
The other cause could be a ignition coil acting up at idle. Above idle it fires.
 
Rating - 0%
0   0   0
Joined
22 December 2020
Messages
7
so if i do the coil pack testing procedure and its between .0 - 1.1 ohms, then ill assume its the injectors?

This just got a lot bigger than i thought. lol

thanks for your help.
 

goldNSX

NSX Prime Moderator
Rating - 0%
0   0   0
Joined
15 May 2004
Messages
6,899
so if i do the coil pack testing procedure and its between .0 - 1.1 ohms, then ill assume its the injectors?
Not necessarily. I could still be the coils. Have a look at the rear ones if they are rusted.
My rear coils started to act up like you described.
 
Rating - 0%
0   0   0
Joined
3 November 2011
Messages
2,913
Location
Saskatchewan, Canada
Did the major service include the timing belt? If so, being off by a tooth can result in vibration and other 'issues'.

However, if the vibration existed prior to the service it might just be the normal C30 / C32 'thing'. The C30 / C32 being a 90 deg V6 does not have an even firing order. The crank pins are offset a bit to help with this; but, its not a complete fix. On my 2000, the vibration is most noticeable when the engine is cold. It is also really only noticeable when you are inside the car. If you open up the engine hatch and check the engine it is not noticeably vibrating. The vibration is not noticeable when the car is in motion and once things are warm the vibration drops below the threshold of being noticeable. I hypothesize that on my car because the vibration is only really noticeable inside the car the firewall is acting as a sounding board and the cold engine mounts are stiffer and doing a much better job of transmitting the existing vibration to that sounding board. As the engine mounts warm up they become more flexible and the vibration falls below the threshold of being noticeable. Its been that way for 10 years.

Since your car is 30 years old, inspect the engine mounts. If the rubber has failed allowing mechanical contact that will certainly result in increased noise and vibration transmission. I know another owner of a 2000 whose front engine mount failed causing some interesting problems. Also, if the mounts have been replaced with aftermarket mounts they likely have a higher shore number which results in increased noise and vibration inside the cabin.

As I noted, my noise and vibration inside the cabin comes with no obvious vibration of the engine. If the engine is noticeably vibrating or shaking at idle that is not normal and at that point I would start looking for problems. However, as an observation, it is not normal for ignition and fuel delivery problems to disappear under load unless you have a fuel mixture problem just in the idle control portion of the fuel system. Check to see if you have any stored fuel mixture error codes in the ECU. Running lean can result in rough operation.
 

goldNSX

NSX Prime Moderator
Rating - 0%
0   0   0
Joined
15 May 2004
Messages
6,899
However, as an observation, it is not normal for ignition and fuel delivery problems to disappear under load unless you have a fuel mixture problem just in the idle control portion of the fuel system.
I guess we have to slightly disagree on this point. :) One of the signs of an igniton coil starting to act up is that is doesn't fire at low rpm but catches up at higher rpm than idle. You can hear this at the exhaust as well. Fuel mixture problems can be caused by many things and dripping or insufficient injectors will mess up the fuel mixture at idle first. The OP stated a long storage time and that's why one of my hints were to check them. I've had the same last winter after not starting the engine for several months (I normally do but was unable to do so), the engine was rough at idle for a few minutes but then the car underwent its well-known mysterious self-healing-capabilities and it never came back. :D
 
Last edited:
Rating - 0%
0   0   0
Joined
3 November 2011
Messages
2,913
Location
Saskatchewan, Canada
I didn't see any reference to the car being in storage for a long period of time, just the reference to significant maintenance and that the vibration problem pre dated the maintenance.

I've had the same last winter after not starting the engine for several months (I normally do but was unable to do so), the engine was rough at idle for a few minutes but then the car underwent its well-known mysterious self-healing-capabilities and it never came back. :biggrin:

When the engine first starts up from cold, it will be in open loop fuel control until the engine reaches the transition temperature where it goes into closed loop fuel control. It is possible that if there is a fuel delivery issue that is resulting in a slightly higher AFR than design during cold idle this could result in rough running and that this problem would disappear once the engine warmed up and went into closed loop operation where the ECU controls AFR to 14.7. I would expect this problem to be present on every cold start. It may also be normal. When cold, the fuel pulse widths may be set to provide an AFR to provide steady operation; but, not necessarily smooth operation until the engine reaches operating temperature.

My C32 is a slightly different animal because in 2000 Honda applied air injection into the exhaust manifold along with relatively fast idle following start up the purpose of which is to bring the catalyst up to operating temperature really quickly to meet the stricter emission targets during the warm up phase. The vibration transmission to the cabin in my car does not disappear immediately as the engine comes up to operating temperature. On very cold morning starts (0 C ambient) the engine will be off fast idle and starting to come up to temperature; but, the vibration persists. The vibration will disappear if I stop the car and then restart it after a few minutes which I hypothesize allows the engine mounts to heat soak a little bit and improve their compliance. My vibration problem is definitely related to ambient temperature. Cold engine starts when the ambient temperature is around 25 C result in almost no perceptible vibration in the cabin. That is why I believe that my particular vibration is related to the change in the compliance of the engine mounts with temperature.

If the OP gets vibration at idle regardless of engine operating temperature or ambient temperature, then they are experiencing something different than what I am talking about. But, keep in mind that 90 deg V6 engines are not inherently smooth engines. If you want a smooth engine, a straight 6 BMW engine would be the ticket, particularly after it dies on you.
 
Rating - 0%
0   0   0
Joined
3 November 2011
Messages
2,913
Location
Saskatchewan, Canada
so if i do the coil pack testing procedure and its between .0 - 1.1 ohms, then ill assume its the injectors?

This just got a lot bigger than i thought. lol

thanks for your help.

All that test does is confirm that the coil windings have not gone open circuit. Failure of the windings by going open is not the normal failure mechanism. The coils can pass the resistance test and still have failure of the high voltage insulation allowing internal or external flashovers and engine misfires. This would probably be the more typical failure mechanism. Internal flash overs are impossible to confirm without elaborate test equipment. However, if you remove the ignition coils examine the nose of the coil that connects to the spark plug. Look for signs of arcing on the nose which would be an indication of external flashover. Unfortunately I presume that the original plugs are now in the garbage because of the major maintenance so you can't examine the insulators for signs of tracking.

Check for stored misfire codes in the ECU which could be a sign of an ignition problem. Significant misfire would normally cause the CEL to flash and should be noticeable. However, the CEL may not stay lit as I believe it requires a persistent misfire with a number of events before it will stay lit. You might have some stored pending misfire codes if you have not passed the threshold to illuminate the CEL. The pre OBDII cars rely on detecting rapid crankshaft speed fluctuations to detect misfire so mild misfire may not trigger an error.

Look at the base of the coil where it mounts to the head. Some mild surface rust is acceptable if it can be cleaned off. Significant rust which causes the exposed laminations to separate or be forced apart reduces the magnetic field coupling resulting in a weak spark and means the coils should be replaced. The coils on the rear cylinder banks are prone to problems with moisture ingress and rusting, particularly if a previous owner liked to wash the engine with high pressure water. If the gaskets on the coil covers have been damaged or the coil covers switched front to back following a spark plug change this increases the moisture ingress and the risk of coil problems.

The ignition coil currents are switched by the ignitor module unit which is a rectangular box with fins on the side mounted sort of above and back from the throttle body. Some are all black and some have silver tops. The ignitor is grounded through two wires in the attached wire harness - the 8 pin side with the attached service test loop. Check to make sure that the ground connection is good - clean metal with no obvious oxidation present. A poor ground can cause erratic ignition performance
 
Rating - 0%
0   0   0
Joined
30 October 2016
Messages
931
Location
Austin, TX
As old guy said, C30 motors aren't particularly smooth even under the best of conditions.

Early NSX ECUs do not have any sort of misfire detection capability so there won't be a trouble code for that on a 1991.

If there's an issue beyond normal not-that-smoothness, I'd suspect either coils or injectors first assuming the plugs have been changed recently. On old cars it's good practice to have the injectors serviced and tested so I'd probably do that either way, however diagnosing bad coils is a bit trickier due to the aformentioned lack of misfire detection capability.
 
Last edited:
Rating - 0%
0   0   0
Joined
3 November 2011
Messages
2,913
Location
Saskatchewan, Canada
Early NSX ECUs do not have any sort of misfire detection capability so there won't be a trouble code for that on a 1991.

My error. You are correct. I was thinking that the 71-76 error codes that use crank speed detection were also in the pre OBDII ECUs; but, on checking I see that the error codes in the pre OBDII ECU in the NSX ended at 59.
 
Rating - 0%
0   0   0
Joined
10 April 2008
Messages
2,347
Location
Northville, Michigan
When we got our 1st NSX back in 2008, I thought we had a rough idle issue.

Another local enthusiast let me try out his (thanks Ryan), and it felt identical......so I decided that's just how they are.

Between that and the transmission it just kind of feels like a race car, so not a problem but a feature :cool:
 
Rating - 0%
0   0   0
Joined
22 December 2020
Messages
7
Hey guys,

Thanks so much for all your input. all makes sense and i guess it a bit of a process of elimination.

With regards to the car - tonight i stayed back and thought i would tackle the easy job first as per GOLDNSX suggestion.

Standing on the right side of the car - i removed the front bank. All coils were in good condition underneath. I metered all coil packs on the front bank and the resistance was 1ohm. (within spec: 0.9-1.1)
I then removed the plugs and all plugs looked good!

I then started on the rear bank. Cyl 1 being closes to the right side of the car - i removed the coil pack and it was HEAVLY rusted underneath. 65-70% of the bottom metal plate was covered in rust. no just surface rust but corrosive rust. i wire wheeled it and the metal wasnt smooth. the rust had messed it up a little.

cyl 2 was ok - just light surface rust. nothing major.

cyl 3 was perfect.

Cyl 1 plug was WET. quite black and dark compared to the other 5 plugs.
so im asuming at the moment its injector or coil related....

Im about to order 6 new coil packs. they are all 30 years old - ill swap them all out and start fresh.

Will update once ive done this.

thanks heaps again everyone.

I'll also inspect the engine mounts too. see how they are travelling.
 
Rating - 0%
0   0   0
Joined
11 July 2014
Messages
1,432
Location
Chicago, IL
Silly question (I am doing some of this work as well). I have never handled coil packs. Do I need to power down the car (disconnect the battery) prior to removing them? When I was a teen I made the mistake of shocking myself across the driveway when I touched the wrong thing during a points change (coil.)
 
Rating - 0%
0   0   0
Joined
8 February 2019
Messages
597
Location
Atlanta, GA
Nah, shouldn't be necessary, but it's never a bad idea. So far the only time I've shocked myself is when I had the alternator positive lug rubber boot off and I laid down a ratchet where the socket happened to touch the lug and the ratchet to a ground point so it arced and gave me a good scare. Just removing the coil covers and coil packs I personally wouldn't bother.
 

goldNSX

NSX Prime Moderator
Rating - 0%
0   0   0
Joined
15 May 2004
Messages
6,899
I then started on the rear bank. Cyl 1 being closes to the right side of the car - i removed the coil pack and it was HEAVLY rusted underneath. 65-70% of the bottom metal plate was covered in rust. no just surface rust but corrosive rust. i wire wheeled it and the metal wasnt smooth. the rust had messed it up a little.
Another point scored for me, lol! :)

You're on the right track or better said you've found the cause with the most likelyhood. Having water on the spark plugs causes exactly those symptoms. They rust due to rain or washing the car. The rust is only an indicator, the water is the culprit. Think about a way to prevent water running down there.

Speedmaster: one test would be to disconnect one single coil with the engine running and see if the idle changes, no need to disconnect the battery. The high voltage is generated within the coil, not before (like in old cars).
 
Last edited:
Rating - 0%
0   0   0
Joined
22 December 2020
Messages
7
Hi Guys,

Sorry its taken so long to get back on and discuss the outcome...

I did end up ordering all new coil packs. I also ordered 6 brand new OEM injectors. The injectors are 30 years old and never been cleaned i reckon also.

The car was deffinately running off 5 cyl. the idle was horrendous. and Plug #1 was so wet dont think at all it was firing on idle.

So i pulled it apart, removed oem OLD coils, Removed oem OLD injectors.

I popped in all new injectors with new seals etc, i then put in all the new injectors.

I crossed my fingers and fired the puppy up and it ran that smooth it was almost hard to believe.

The cars idle when cold or warm/hot is flawless.


Im trying to work through a few issues one by one - bit by bit - so this one was a massive load off my shoulders.

The engine is super smoth and the car drives great. I can confirm was coil pack CYL #1 .


With regards to my other issues im trying to sort...

2) When you rev the car when stationary it vibrates slightly at 2000rpm.

When you take off its smooth as - when you go through the 2000-2200rpm range you feel some vibration in the seat etc but only for a second or two then goes away and smooth as no issues.
for this it could be the natural harmonics of the engine and or mounts. I will back off all engine mounts and re-righten in the correct sequence according to user manual and see what that does.


3) when you put key in the ignition - and turn the ignition ON (but not start the car) there is a LOUD af CLICK CLICK CLICK CLICK coming from what i believe is the fan core unit under the bonnet.

When the car went in for a major service i spoke to honda and explained the FAN MOTOR for the AC/Heater didnt work on settings 1, 2, 3... only on FULL SPEED. They said "oh fan unit has an issue. They ordered brand new unit and fitted it.
When they tested it, same thing happened. They then said it was the control box. I had them remove it and took it to an electronic repair centre. They found the fault, fixed it and gave it back. re-fitted and BANG - everything works perfect.
The day i picked up the car from honda was fine. - A few weeks after, the CLICK CLICK CLICK CLICK started. It clicks about 5 times then goes off.

This is issue 3 i need to sort.

4) Even though honda did the MAJOR service - there was a axle seal leaking. After they gave the car back i saw some oil on the floor when parked for a few weeks. Sussed it out - and they never attended to the axle seal and replaced it.
I have ordered new axle seal with al new CV boots and REDLINE grease - will be attending to this very shortly!


5) Rear antenna clicks when goes up.... never did before service but after the service the radio and the antenna is playing up. The radio did work BEFORE i took it in, then after i got it back - it no longer works.

Unsure what this is also.



If anyone has any input about these points listed, please let me know im all ears and would love to discuss it.


On a good note: ive always been obsessed with Hondas. I built an s2000 race car - have another 2 s2000's, a DC2 type R also and they are incredible. But for a car that was built 30 years ago, i cannot believe how perfectly engineered this car is. The NSX is as raw as it gets. I cant wait to get it on the road properly.

I have fitted V3 coils and have a set of NSX spec TE37 ready to go on.

I also have some parts on order from SOS so cant wait to get that going either.

I have driven hundreds of cars, and we own some other more modern performance cars, but nothing puts a smile on my face like this thing. I prefer to drive this than anything else ive ever driven. Almost hard to believe how good they are. at the time they would have been 20years ahead of of everyone else. New performance cars today dont give you the road feedback this does. new cars are becoming more and more numb.

Im obsessed with this thing. its incredible!

Thanks for everyones input. legends!!!
 
Top