Engine stalling

[mrtexas]

Started up the 99 nsx on a cool morning last Tuesday here near Houston, perhaps 50F. Engine not fully warmed up.
All was well but putting in clutch at stop light the rpms dipped below 600rpm and the
engine died. Noticed the idle rpm spiked below 600rpm a couple times but
quit only once. What could be causing this?

 

[jwmelvin]

Unmodified car? Dirty throttle body?

 

[mrtexas]

Unmodified

 

[Old Guy]

If your car was non DBW, I would start with 'check the IACV' (or if you prefer EACV). But, yours is DBW so I think the best thing would be to get the service manual and check the trouble shooting procedure for the idle control system on DBW cars. There are a bunch of inputs to the ECU (clutch switch, neutral switch, brake switch, TPS? ......) that affect the operation of the idle control system. The ECU uses those inputs to go into closed loop idle control where it monitors the actual engine speed and controls the throttle to keep the engine speed constant at the idle setting. The combination of clutch in, brake pedal depressed should put the ECU into closed loop idle control once the engine speed drops below the idle threshold. I would hazard a guess that the switches might be inoperative or operating intermittently; but, that is just informed speculation. Best to go through the trouble shooting procedure for the idle control.

If you were having other driveability problems, I would consider the throttle body as jwmelvin suggests; but, if the car has been running well and this came out of the blue then I would check out the operation of the idle control system.

 

[mrtexas]

Will check out clutch and brake switch signal on ecm 11-107, 11-125, 23-310, and 11-127 in service manual

 

[Scrapdog2grand]

Will check out clutch and brake switch signal on ecm 11-107, 11-125, 23-310, and 11-127 in service manual

Clean the throttle body and do an idle relearn procedure, you should be good.

If not, tight valves can cause a high Map sensor reading, normally causing a stall coming to a stop(as will the above) or at idle.

btw - The DBW eliminated and idle air control system and fast idle valve.

 

[mrtexas]

How to Link?

 

[Scrapdog2grand]

How to Link?

This one is about as good as it gets https://mobiloil.com/en/article/car...-yourself/proper-throttle-body-cleaning-guide
Kaz also has some NSX specific blogs on NSXCB but I couldn't find the one on TB cleaning.

There are you tubes and you can use for on car cleaning, the service manual, and you can also remove the throttle body for cleaning if you have some tools and are handy.

The idle relearn, is removing a ECU fuse to reset the ECU and let the car run and come up to operating for a certain amount of time. The procedure is outlined in the service manual that should be available for download here on prime.

 

[Old Guy]

The DBW eliminated and idle air control system and fast idle valve.

Correct that the DBW eliminated the Idle Air Control Valve (also called EACV). The DBW cars still have an idle control system in the ECU; however, rather than opening and closing the IACV to control the idle speed the system opens and closes the throttle plate servo motor to control idle speed.

The idle relearn, is removing a ECU fuse to reset the ECU and let the car run and come up to operating for a certain amount of time. The procedure is outlined in the service manual

The idle speed setting procedure on DBW cars does not require removal of the clock fuse which is the procedure used to erase fuel trims and stored error codes. The idle setting procedure does require allowing the engine to come up to temperature, then stop the engine and short the service check connector before restarting the car, and then setting the no-load idle speed to 600 RPM with the idle adjustment screw using an accurate external tach or an OBDII scanner to read RPM. The SC connector is then removed, you run the engine up to 1000 RPM and then slowly ease up on the throttle. The engine is supposed to stabilize at 800 RPM on manual cars. Honda is non specific about what to do if the engine does not stabilize at 800 RPM. I expect that you repeat the process and if it doesn't work out then check to see if the idle control system has problems.

If you want, you can run through the idle set up procedure to confirm that it is set correctly. However, in my opinion I would not mess with the idle adjustment screw unless I had exhausted all the other possible causes of an idle control problem. As I recall, the idle adjustment screw is covered in a greyish sealant which has to be removed to get at the screw. Honda clearly does not want you fiddling with the screw.

 

[nsxtacey]

I have the same problem when the car is warmed up but only happens if it is in neutral. Once in gear it does stays above 1k rpm. I had it engine shut off twice and a nsx mechanic thought it was the fuel pump or is it more likely the throttle body?

 

[Old Guy]

I have the same problem when the car is warmed up but only happens if it is in neutral. Once in gear it does stays above 1k rpm. I had it engine shut off twice and a nsx mechanic thought it was the fuel pump or is it more likely the throttle body?

What model year?

If it is pre DBW, I would be checking the IACV / EACV first. If the stalling only occurs when in neutral, check the neutral switch connection to the ECU.

 

[Larry Bastanza]

Based on the OP's original post, First thing I would do is clean the idle passage in the throttle body. I have had many NSX's have this issue, and a clear idle passage has corrected it for me many times.

HTH,
LarryB