Deleted old thread/not yet solved/engine stall

[NSX-Racer]

Problem since autumn 2002: Release throttle after raising the (warm) engine to over 7000, rpm drops under 500, then rests stable at normal 850 rpm idle (ca.). Not a big problem while you're standing. But: In race situation (braking hard after a long straight, clutch pressed) the rpm drops sometimes so low that the engine stalls. The longer the braking time the more likely the problem occurs. No engine check light, no error code in memory afterwards. Engine starts again with no problem. No decrease in engine power and behaviour.

The car: '98 cp., 3.2 l, 6 speed - about 120.000 kilometers - race only since about 100.000 km (about 24.000 race km all over). No engine mods, but no cats, K&N replacement filter, Sachs race clutch with Comptech light flywheel, Porsche brakes (993 turbo front, 996 GT 3 rear), Dali race sway bars, Eibach pro springs, Bilstein HD shocks.

Had nearly all the above mods already before the problem occured for the 1st time, then changed sparks, checked all hoses, belts, fluids etc and found no mistake. The (4?) O2 sensors seem to be okay (there was also no problem after the cat removal some years ago). There has been no modification between the last race event with no stall problem and the first event with that problem.

The car is none of those '98 NSX where a TSB was released to change the ECM (I checked this with Honda Europe - although my car is in the VIN range - no. 006 - this TSB is only for cars sold in America).

My mechanic has no big idea - I'm puzzled too - what could I do?

 

[Larry Bastanza]

NSX-Racer,

If you have not done so already, I recommend you have the throttle body cleaned. Especially the idle bypass passage.

HTH,
LarryB

 

[snapper]

NSX-Racer,

If you have not done so already, I recommend you have the throttle body cleaned. Especially the idle bypass passage.

HTH,
LarryB

That would be my first guess too.

 

[daveh]

flywheel!.a lot of times the pcm cannot command the idle control valve for the difference in inertia with a lightned flywheel.just as it will wind up faster it will also slow down faster .It's less of a flywheel!!!Bump up the idle speed about 100rpm and clear the pcm.try it.you'll like it

 

[NSX-Racer]

To Dave: Theoreticaly you're right, but as I mentioned before I had light flywheels (in different weights) long before the problem occured.

To the others: Thanks for the hint - that was exactly the next point on my agenda. My mechanic had already ordered new seals for the throttle body to rebuild it after taking apart and cleaning. Hope that helps and hopefuly there's no other more serious reason for the problem.

 

[snapper]

Make sure your tech cleans the idle bypass. Often they overlook it when cleaning the throttle body.

 

[DanO]

In race situation (braking hard after a long straight, clutch pressed) the rpm drops sometimes so low that the engine stalls. The longer the braking time the more likely the problem occurs.

Maybe a fuel delivery problem under braking?

 

[Tantheman]

Just had my oil change today at South Coast Acura and waited for it. I noticed the mechanic took my car out for a test drive and none of the other cars. So why he was out driving I asked another mechanic if that was standard to test drive before an oil change. He said no. Due to my exhaust modification I could hear him VTEC the engine in the distance.
Anyways upon getting the car back and driving back home about 5 miles away. I noticed this same situation where the RPM really goes below idle when I brake.
Complained to service manager about my discontent with the mechanic taking the car for an evaluation drive prior to the oil change. Now I have to go back and deal with this situation too.

Tan

 

[NSX-Racer]

Update

Sorry folks - problem still exists. Throttle body was cleaned (yes, the idle bypass too), new seals and rebuilt. Idle seems to be a bit more stable but the rpm always drops beneath 800 rpm after releasing the throttle - also when the car is standing in neutral - and then rises to about 900 rpm. Sometimes it stalls also in that case - not only under heavy breaking.

My tech suggests that the idle control could unit (in the throttle body) could be bad after 5 years and 121.000 km (more than 20.000 km on track) so he would have to change the whole throttle body. Does this make any sense to you?

Is there really a simple way to rise the idle rpm without irritating the ECU? If yes, where and how? Just to clarify: I'm aware of the fact that this problem may not exist with a heavy stock flywheel - but as mentioned before the engine run fine for years with light flywheels.

Any hint is appreciated!

 

[Larry Bastanza]

If you have excessive money to burn, get the throttle body. They are mucho $$$$$$$$$$. Actually I think you should investigate and look for any small vacuum leaks first. Your description almost sounds like the engine is "hunting" at idle.


Did I understand you correctly about the idle going to 900?

HTH,
LarryB

 

[NSX-Racer]

No - Larry - I have no excessive money to burn - do you have an idea of the amount for the throttle body? And does it make sense to buy it?

What do you mean by "hunting" the idle and vacuum leaks? We've checked all hoses and connections. Is there a special place or thing we should search again?

And - yes: If the engine doesn't stall it goes up again to about 800-900 rpm and stays there when I'm not on the gas.

Once again the question: How can I adjust the base idle without puzzling the ECU? Didn't find it in the FAQ.

TIA
Wolfgang

 

[Larry Bastanza]

OK, by "hunting" I meant the idle going up and down at some frequency, lets say between 600 and 900rpm. It sounds like it is NOT doing that, based on your response.

What year car? It if is not a DBW (pre-1995) there is an idle by-pass adjustment screw. It is right on top of the throttle body, on the right side of the intake about 1 o'clock, looking from the drivers side of the car. It is normally not adjusted and it is probably painted over. You will have to crack and clear the paint. As with all adjustments, record where you start, in case it does not solve it, and you want to return it to it's original position.

I am not 100% sure, but the last thread I read about a new throttle body was $1700+US, although I think this was a DBW version which is more expensive then the cable unit (pre-1995)

HTH,
LarryB

 

[PettittsAuto]

Idle problem

This might be a shot in the dark but a couple of years ago I had a 1997 NSX with a hunting problem at idle and it was the neutral position switch in the transmission that was causing the problem. It took me a long time to find the problem. What was happening was when the car would sit at idle it was ok until you touched the shifter knob. All it took was the pressure of your hand resting on the shifter and the idle would start hunting like crazy and the car would eventually die. It would be easy to check just warm up the car and move the shifter a little and see if the idle starts to hunt. just a thought.

Bruce

 

[Larry Bastanza]

Bruce,

WoW!! Do you know the reason why the nuetral switch would cause it?? Electrical issue??

There's "one for the books"

Thanks,
LarryB

 

[PettittsAuto]

Larry, When you shift the car into gear the neutral position switch senses a load and tells the ecu to compensate. Well the switch in the car I worked on was way too sensitive and all you had to do was touch it and it would start trying to compensate. It was a wierd problem, took me a couple of days to figure out.

Bruce

 

[Larry Bastanza]

Thanks Bruce,

At least it makes some sense, even though it was tough to figure out.


LarryB

 

[Black&Tan97Tnewportbeach]

Just blast the sh!t out of it with a $5 can of THROTTLE BODY cleaner, I do mine every week or two because my current turbo leaks oil & ??? into the intake and clogs it with yuck, before I figured out this trick I thought the NSXM turbo was slowly killing my car since it couldn't hold an idle at a red light, now I blast it every so often and it idles like a stock champion!!! GooD Luck!!!

 

[NSX-Racer]

Thanks for all the hints, folks!

Larry: It's a '98 cp with DBW - so I have to ask the question again: Is there a way to adjust the base idle without confusing the ECU?

The idle is not "hunting" (or "sawing" as we call it here in Germany) but I noticed this hunting when I tried to raise the idle by manipulating the throttle control in the spare tire compartment. I did put a piece of Gaffa tape between the wheel and the point where the wheel comes to a rest when you release the throttle (sorry for my bad technical english) so the wheel stops a bit "higher" than normal. That seems to drive the ECU mad. You'll get "hunting" and maybe an engine check light.

Black&Tan '97: Cleaning the throttle body: As I wrote before that was already done just before the last event (May, 31.)

PettittsAuto: Good hint - but the engine is not hunting and it can stall in neutral and in any other gear - usualy you're never in neutral on the track.

Just another thought brought to me by a Honda dealer (we have no Acura dealers here): Can the timing belt jump for one or two teeth and cause the trouble I have? The belt was changed about 20.000 km ago and the engine shows no sign of power loss or other unusual behaviour.

 

[TypicalNSX]

nsx_racer, did you ever get this issue fixed? i am having the same problems. please advise. . .

 

[NSXFRIEND]

Problem since autumn 2002: Release throttle after raising the (warm) engine to over 7000, rpm drops under 500, then rests stable at normal 850 rpm idle (ca.). Not a big problem while you're standing. But: In race situation (braking hard after a long straight, clutch pressed) the rpm drops sometimes so low that the engine stalls. The longer the braking time the more likely the problem occurs. No engine check light, no error code in memory afterwards. Engine starts again with no problem. No decrease in engine power and behaviour.

The car: '98 cp., 3.2 l, 6 speed - about 120.000 kilometers - race only since about 100.000 km (about 24.000 race km all over). No engine mods, but no cats, K&N replacement filter, Sachs race clutch with Comptech light flywheel, Porsche brakes (993 turbo front, 996 GT 3 rear), Dali race sway bars, Eibach pro springs, Bilstein HD shocks.

Had nearly all the above mods already before the problem occured for the 1st time, then changed sparks, checked all hoses, belts, fluids etc and found no mistake. The (4?) O2 sensors seem to be okay (there was also no problem after the cat removal some years ago). There has been no modification between the last race event with no stall problem and the first event with that problem.

The car is none of those '98 NSX where a TSB was released to change the ECM (I checked this with Honda Europe - although my car is in the VIN range - no. 006 - this TSB is only for cars sold in America).

My mechanic has no big idea - I'm puzzled too - what could I do?

I am not a mechanic but have you changed the fuel filter and coils? How about cold position sensor & throttle positioning sensor? I am curious under what circumstance in racing you need to idle the car while braking, why not let the car in gear while braking? Also you might want to pull the spark plugs back out and reseat them, is there oil on the spark plugs? Any loose grounds anywhere?