Stalling with A/C on.

[NSX2NV]

Due to the high temps yesterday I had my A/C on high and had a problem with the car stalling twice. A few times when coming to a stop I put the car in neutral and the RPM's went down to 4-500 and then back up to idle. Then at a left turn the car shut off and the same at a red light.

I had the stereo at low volume and everything else was off (cuise, wipers, lights etc) I do have an aftermarket stereo with two large amps but they have a capacitor that stores power installed.

Is the idle set to low on the car? I have noticed that the RPM's drop below normal idle RPM's when stopped sometimes but this is the first time the car has stalled. Is there a problem with the engine or am I just putting to much load on the engine with the A/C at full and the aftermarket stereo..

Thanks

Johnny

 

[Lud]

What is your warm idle RPM with the AC turned off, and is it steady?

 

[NSX2NV]

Idle at warm is 600 RPM. When I turn the A/C on the RPM drops to 2-250 RPM and then goes back to approx 550-600 RPM after 1-2 seconds.

Once the A/C is on full at idle the RPM's flutuate from 500-600 RPM.

Is this Normal?

 

[Larry Bastanza]

I think your base idle is too low, 800 +/-50 rpm is spec. You can raise the idle by the adjustment screw once you remove the paint, since it is painted in position at the factory.

On Line service manual page 11-84/86

But first, how many miles on the car? Has the throttle body ever been cleaned??



HTH,
LarryB

 

[NSX2NV]

My car has approx. 31,000 miles on it. Should I have my local dealer look at it to make sure the idles are to low? Or should I be able to adjust the idle myself.

Thanks

 

[Briank]

NSX2NV

You really can't adjust the idle on an NSX the computer controls the idle but there are things that need to be right before the computer can do its job. There is a base setting that needs to be right and from what I can tell from the service manual 11-66 there is a signal that tells the couputer the A/C is on and if that is not present that is the #1 cause of low idle with the A/C on.
If you are not famular with working on you X you may have to take it in.

BrianK

 

[Larry Bastanza]

Briank,

Why do you say there is no idle adjustment? It is clearly described on page 11-84. It is sealed with paint at the factory, but it can be adjusted. It is a typical air bypass line around the throttle body in the cable throttle models (1991-1994). The 1995+ with TBW have a more elaborate setup, but still they have a similar adjustment.

HTH,
LarryB

 

[Briank]

Larry

Yes there is an idle adjustment screw that can be changed but:


The EACV (Electronic Air Control Valve) controls the idle. Setting the idle speed per the procedure in 11-84 just sets minimum air bypass to get the 650 +- 50 RPM with the EACV disconnected. The actual active control is done by the EACV which is controlled by the computer to get the 800 +- 50. which is not adjustable and will even cause a check engine light if not working properly.
If you notice once you reconnect the EACV there is no futher adjustment. 11-85

You may have noticed how well the NSX holds its idle speed even with constantly changing loads, i.e.: A/C compressor and changes in electrical loads this is not possible with a fixed idle setting like in the old carburetor days.

Brian

 

[Larry Bastanza]

OK,

With that said, I would think the adjustment procedure should be run to insure the "base idle" is correct, no??

Is seems the EACV may be capable of working "up" from 650rpm (I think the range is probably very limited from the air flow perspective).

Good Topic

LarryB

 

[NSX2NV]

I'm taking the car to my mechanic to have the base idle checked first.

Could the extreme heat cause the car to pull to much load resulting in stalling. On days when it hasn't been as hot with full A/C on the car never stalled.

 

[Larry Bastanza]

I think the car should be perfectly capable of dealing with the heat we are in.

But... if something is out of adjustment or not competely functioning correctly the effect could be is stalls due to the heat.

How hot is it up there anyway?? Here we are +90F and very humid


HTH,
LarryB

 

[NSX2NV]

The day I had the stalling problem it was 95 degree F out plus the humidity. It has since cooled down and I haven't has a stalling problem.

Going to get it checked out just in case.

 

[NSX-Racer]

Okay, BrianK and Larry - here we come to a point where I have been left puzzled in an older thread (adjusting idle on a DBW car). What Brian wrote here was exactly the same that my mechanic said and Larry worte in the old thread that it can be adjusted (as he stated here too).

I'm still dealing with my pre war problem that my '98 cp. rpm drops in the cellar when I release pedal after full throttle (no matter what gear or in neutral) , then goes up to the appropriate 850 rpm - but sometimes it stalls, especialy under heavy long braking with clutch pedal pressed on the track.

Now: Can I adjust the base idle by disconnecting the EAVC plug, starting the engine, adjusting the idle bypass screw on the throttle body, putting ignition off, replugging the EACV and starting the engine again (in this sequence, that was the procedure Honda Germany told me as far as I can remember)? Or should I do that in a different way?

And: Can that solve my problem? Otherwise I may have to buy a new throttle body for about 1,500 Euro (yes, throttle body and idle bypass valve have been cleaned, vacuum hoses have been checked 3 times, no error code).

 

[Briank]

NSX-Racer

I would not buy a throttle body


The first thing I would check is the dashpot system 11-117, 11-118 it slows the closing of the throttle durring shifting and deceleration so the engine dosent stall.


If that is OK then you need to trouble shoot the EACV and the signals that the computer uses to properly control the idle. Looking at my 1991 service manual 11-69 there is a whole list of things that can mess up the idle control without causing a check engine light. I would recommend checking every thing listed starting with the Alternator FR signal on the list.


BrianK

 

[Larry Bastanza]

I agree with Brian.

Also if I recall the 1997+ cars had this characteristic of the revs actually rising slightly betweeen shifts, I have seen this in a 1997. There were many complaints about it on this forum at one point.

It seems to be a function of lowering emissions to leave the throttle hang open for a second so you do not end up with instant vacuum in the intake, increasing emissions. Does your car do this??

This sounds like a function of the dashpot Brian is refering to. Also does the 1997+ (maybe 1995+ TBW) have the dash pot?? With TBW I would think the ECU would handle that, not sure.



LarryB

 

[Briank]

Larry

Yes, Dashpots were one of the first of many things added to carburetors to reduce emissions. When you close the throttle on a carburetor the high vacuum draws in lots of fuel making for a very rich mixture not a good thing for emissions but the popping and occasional back fire when running open exhaust was cool. The dash pot held the throttle slightly open for a short time after you let off the gas to let the engine slow down and the high vacuum subside. It also helped keep automatic transmission cars from stalling. In a modern fuel injected engine holding the throttle open for that reason is unnecessary. The computer calculates the correct amount of fuel based on throttle position and manifold absolute vacuum and other info so when there is lots of vacuum i.e.: the throttle is closed and the car is pushing the engine the computer just stops firing the injectors all together.

My guess on why the X has a Dashpot is that the EACV would have trouble controlling the amount of air to bypass the throttle when the vacuum is very high. So by holding the throttle open and letting the high vacuum subside the EACV does not have to try to control the amount of air bypass at a high differential pressure.

Briank

 

[NSX-Racer]

Larry, Brian - thanks for your input.
In my dictionary "Dashboard" is translated as the german word "Armaturenbrett" which is the instrument panel in front of the driver. I guess this is not what you mean. So where can I find the dashboard you are writing of?

BrianK: Can I really take the U.S. service manual of a pre '98 NSX to check my '98 german model? The problem is that the '98 manual would cost 390 Euros here but it's not in stock at the moment.

The idle behaviour of a U.S. NSX may be different than an european model. They have different ECUs due to the different emission and noise restrictions. In my special case: My car is theoreticaly in the VIN range for a TSB for an ECU change (referring the idle control) but Honda Germany asked Honda Japan and they said, the german ECUs need not be changed.

Any help appreciated - couldn't find anything in the FAQ that helped.

 

[Briank]

NSX-Racer

A Dashpot is a diaphragm type device that slows movement, kind of like an air cushion. When the throttle closes it pushes on a diaphragm that has a restricted outlet, the trapped air escapes slowly letting the throttle settle gently on to it stop. I found the German translation Dämpfungszylinder.

If you have one it will have a small hose connected to it and to the flexable rubber hose between the throttle body and the air cleaner box

I hope this helps, let me know and I can send a picture of the one on my 91.

Briank

 

[NSX-Racer]

Yipiie - stalling problem solved

Thanks to BrianK, Larry and the online service manual (which is for the '91 but some basics are the same as for my '98) my idle is now okay again. Seems that my mechanic and me have dealt with the wrong screw and the wrong procedure. Plus: The idle bypass screw must have been nearly closed.

The right procedure: Warm up the engine, all load (fan, A/C stereo etc.) off, then engine off. Pull the EACV plug (beneath the throttle body, 4 or 5 pins AFAIK). Start engine with slightly pressed pedal. Release pedal. Adjust idle on the idle bypass adjust srew (on the '98 model it looks to the driver side, you nearly can't see it from above the throttle body). rpm should be 650 +/- 50 rpm. Engine off. Pull clock fuse for at least 10 seconds (ECU reset). Start engine, look what happens. rpm should be stable at around 850. Rev up to high rpm, release pedal quickly. rpm should not fall under 850. In my case it rests a second or so at about 1,100 and then goes down to normal idle - for me and my track car quite okay.

Lud: Something for the FAQ?

Dashpot etc. seem to be no problem in my case. Thanks to your help I saved about $ 1,700 for a new throttle body - great!