Shaky feeling at idle

[dustin]

Ok, I have done a search for this and read all of the threads (rough idle, etc), including the FAQ. So don't rip me a new one I know this is a common complaint, but I think that perhaps my car might be a little different.

'94 NSX. Now with ~69k miles.

At idle there is a distinct vibration throughout the car. Can be felt in steering wheel, shifter, gas pedal, and just in the car itself. A few passengers have even commented on it. You can see the steering wheel vibrate a bit if you watch carefully.

The vibration is "random-feeling" enough that it almost feels like a misfire-induced vibration. However, if I listen to the exhaust I do not hear misfire, and the engine sounds normal at idle. Idle itself is 100% stable, no dips. Also, it feels the same whether the car is cold or warm.

I replaced the spark plugs with brand new OEM units with proper gap. I also replaced the air filter. This did not change anything (I did not really expect it to, either). I also used an ohm meter to check the coils, and they all were within spec.

As recommended in the FAQ and other threads, I got some throttle body cleaner and cleaned the entire throttle body assembly along with the air box duct. Interestingly enough, this smoothed out the idle and removed about 75% of the vibration, but it quickly returned over a period of a few days.

Also, this is not the normal 1400rpm NSX vibration. I can feel that too if I hold the car at 1400rpm. That does not bother me. What I am describing is not as pronounced as the "1400rpm" vibration, but it is also more "random-feeling" as I have described above.

I know people say this is part of the car's personality, but I just do not like the feeling of it. My (to soon be sold) CRX with a self-built B series motor (forged pistons + piston slap galore), hard poleurethane motor mounts, and lowered compression feels much smoother at idle than the NSX. In fact, every correctly operating vehicle I drive feels "smoother" at idle than the NSX. I love everything else about the car, but this bothers me every day I drive it.

Any ideas?

Dustin

 

[201]

I have the same problem. I had the whole car checked out 2 months ago and the only thing the mechanic can come up with was the engine mounts being too old. Everything else as you said you did on your car was excactly what I did with mine.

 

[matteni]

Over the course of the last year I too have done the timing, checked the coils, timing belt stuff, carb cleaner for the airbox/throttle body, fuel filter, plugs/wires with OEM, and have tightened all the engine mounts. The car runs perfect off idle but feels like it "stutters" every 1-2 times/seconds on idle. I run 93 octane gas only.

I am running the Dali HOT chip and don't know if that has anything to do with it - but I doubt it.

The trick is to spend as little time at idle as possible. It is hard to get to nearly 90 hp/l out of a V6 without some drawbacks.

Unfortunately - I am not the original owner of the car (purchased used in 97) so I can't comment on if the idle changed during the first 6 years.

 

[nsxtasy]

Dustin,

You might try driving one or two other NSXs in your area to see if you notice the same thing. Preferably newer ones.

 

[Edwardo]

Dustin,

If you were to test my car you would experience the same roughness as your own car. I have the typical vibration at cold idle and a less pronounced vibration at warm idle.

My car has up to date service etc..etc...

My car is older and has more miles than yours so do not take too much comfort in what I am saying. I may have it too.

 

[Zishan]

Ditto, my car idles slightly rough also.

 

[Smoothaccel]

Hi Dustin, my car has about 64k miles and it does have a rough idle. If I slowly raise the rpm it vibrates a little more before it stops vibrating around (1500 rpm, I think). I have accepted it to be normal since my car is maintained properly and some others have the same issue.

 

[NSXCessive]

My '91 also seems to suffer from this problem, I just had a major tune up done. Spark Plugs, Air Filter, Timing Belt, Water Pump as well as various other things.

I thought this would go away after my service, but same problem. Doesn't seem to matter what I do it has the same problem at idle a pronounced vibration cold start, and far less when warm. I've never had a problem so I've considered this to be normal as well.

Do the 3.2L Manual owner's have the same problem? I believe that would be '95+ owners? Anyone care to comment?

 

[1BADNSX]

Could this be the timing belt off one tooth on one of the cams? Everybody with the problem please reply if the change occured after a timing belt change.

Larry, please comment.

 

[nsxhk]

You might want to try cleaning your throttle body and the EACV. Those 2 parts get dirty quite easily when using after market air filter.

Henry.

 

[Larry Bastanza]

Well,

Based on what I am hearing this does not seem to be timing belt related. (Hard to diagnose vibrations via the internet ). I also get a very slight vibration at 850rpm.

If I sit in the car with my hands off the wheel, I can see a very slight vibration. One thing you can do is place your hand on top of the center engine cover (the VTEC plate) and feel for vibration, mine is very smooth at WARM idle, but I still get the vibration I mentioned in the wheel at WARM idle.

My thoughts on this are "Do not sweat the small stuff" . It is not really a luxury car, was never meant to be one.

To be sure though, Ken's advise is right on, drive another one and compare. At least you will sleep better.

HTH,
LarryB

 

[Silver F16]

Get your valve clearance checked. IF they are off, it may intensify the inherint NSX vibrations.

 

[true]

Definetely NOT timing belt related. If a cam was a tooth off, it would be immediately apparent...

Not much seat time in an NSX, but I have considerable in the Honda insight which is a 3 cylinder and shook terrible at idle right from the factory. The idle never hunted, but it would shake exactly as Dustin describes. It was pretty bad and I just assumed that was one of the prices to pay for a car such as the Insight. One thing just dawned on me though...3 cylinder Insight, 6 cylinder NSX. My CRX and GSR are always perfectly smooth with 4 cylinders....it may simply be a function of these engine's design (3 cylinder/dual 3 cyl) and resonant frequency at that RPM. I'd imagine the NSX is a little less because it has 2 banks to semi-equalize..but the Insight was really bad. It may be pretty far fetch..but it's an idea if the NSX's from the factory are guilty of this behavior.

 

[rrwildman]

Dustin:

You failed to mention the most important information relative to ANY problem:

Has it always happened, and if not, when did it start and what, if anything, preceded the change.

That aside, "IF" what you're feeling is what I've felt in every NSX I've driven, it is the camshaft lift and duration which causes this, and it is absolutely normal. Some have claimed their NSX idles as smoothly as an Accord. I don't believe a word of it, and just figure they aren't very sensitive to the vibrations I'm referring to. (Again, if you think your NSX idles perfectly smoothly, just set a cup of coffee on the console and look at it.) IMO, there's no way that an NSX engine can possibly idle as smoothly as an Accord (or my CRX) with the stock camshafts in it. It's not like a Hemi or something. Just try to associate that slight vibration with the engine's magnificent power band characteristics, and you'll come to appreciate it instead of being annoyed by it.

Richard
'93 Blk/Blk

 

[NSXCessive]

Wonder if this might be realated to the harmonic ballancer? Does anyone with a 32C motor have the same problem? That would be '95 Manual and UP+?

 

[nsxtasy]

Does anyone with a 32C motor have the same problem? That would be '95 Manual and UP+?

The 3.2-liter engine was introduced in '97, not '95.

 

[dustin]

Has it always happened, and if not, when did it start and what, if anything, preceded the change.

No, it has been like this since I bought it, but that was only 6 months ago.

That aside, "IF" what you're feeling is what I've felt in every NSX I've driven, it is the camshaft lift and duration which causes this, and it is absolutely normal. Some have claimed their NSX idles as smoothly as an Accord. I don't believe a word of it, and just figure they aren't very sensitive to the vibrations I'm referring to. (Again, if you think your NSX idles perfectly smoothly, just set a cup of coffee on the console and look at it.) IMO, there's no way that an NSX engine can possibly idle as smoothly as an Accord (or my CRX) with the stock camshafts in it. It's not like a Hemi or something. Just try to associate that slight vibration with the engine's magnificent power band characteristics, and you'll come to appreciate it instead of being annoyed by it.

This makes me feel a lot better. I guess I can quit trying to "fix" it