: Engine Stalling at traffic light



kevinK
02-05-04, 01:00 PM
I have a 98 Sedan Deville with 108K. It was running fine except occasional stalling when waiting for traffic light. It is stalling more often now. At traffic stop, the idle RPM is 600-625 for 10-20 seconds, then drops to 550 and die. If I put the gear on P or N, the idle RPM will stay at 600-650 and no problem. There is no other code detected except engine stall code. The only repair was changing alternator. The other symptom is sticking gas pedal, for which I read some GREAT post here on how to cleaning the throttle valve. I will clean it this weekend.

Thanks very much in advance for any suggestion.

Kevin

BeelzeBob
02-05-04, 04:07 PM
I have a 98 Sedan Deville with 108K. It was running fine except occasional stalling when waiting for traffic light. It is stalling more often now. At traffic stop, the idle RPM is 600-625 for 10-20 seconds, then drops to 550 and die. If I put the gear on P or N, the idle RPM will stay at 600-650 and no problem. There is no other code detected except engine stall code. The only repair was changing alternator. The other symptom is sticking gas pedal, for which I read some GREAT post here on how to cleaning the throttle valve. I will clean it this weekend.

Thanks very much in advance for any suggestion.

Kevin

Since the gas pedal is sticking the throttle body is likely pretty cruddy. If it gets that dirty it can completely block the air flow past the throttle blade. The idle air control system that controls the idle speed depends on a certain amount of "fixed" air to come past the throttle blade for the engine to idle. Then it adds a controlled amount of supplemental air via a separate passage to control the idle. The throttle body may be dirty enough that the idle air control cannot provide enough air to idle on, hence the stall.

Clean the throttle body thoroughtly. You don't have to remove it, just hold the blade wide open and spray with carb cleaner and scrub with an old toothbrush. Do the perimeter of the throttle body bore where the blade is in close proximity at idle and the back side of the blade. I believe that there may be a small hole in the throttle blade on that application....if so, clean it out, if not, chalk it up to my poor memory. Don't worry about all the throttle body and the intake manifold or anything else.....crud there is normal and won't hurt anything.

Disconnect the negative battery terminal for 30 seconds after cleaning the throttle body to reset the idle learn offsets (probably pretty large with a dirty throttle body) so the idle system can start from the clean baseline. Drive the car in a closed area for a few minutes to let the idle speed control system react to the clean throttle body as there may be a surge or stall at first.

This should clear up both problems.

BTW....the stall occurs in drive because the engine is loaded more in drive and if there is a lack of airflow then it could stall there easier. In park, there is less load, so the available idle air is enough.

kevinK
02-05-04, 07:12 PM
Thank you very much, bbobynski.

As usual, your advice makes a lot of scenes and is highly appreciated.

I will clean the throttle this weekend and let everybody know the result.

I may also do a fuel injector cleaning using the BP44K (pouring into the intake manifold OR just pour it into the gas tank). What is your opinion on the BP44K cleaning? I have already bought it.

Thanks again.

Kevin

BeelzeBob
02-05-04, 09:36 PM
Thank you very much, bbobynski.

As usual, your advice makes a lot of scenes and is highly appreciated.

I will clean the throttle this weekend and let everybody know the result.

I may also do a fuel injector cleaning using the BP44K (pouring into the intake manifold OR just pour it into the gas tank). What is your opinion on the BP44K cleaning? I have already bought it.

Thanks again.

Kevin
Keep the BP44K on the shelf to use as parts cleaner one day. It doesn't belong in the fuel or the engine.

The only reason to use any sort of solvent or "top engine cleaner" is to soften carbon to clean the chambers....something that can be accomplished MUCH easier by just doing an occasional WOT blast thru the lower gears.

Solvents can harm fuel pumps and injectors. I have no experience with the BP44K stuff so I cannot comment on it's toxicity to fuel pumps but I would personally never use it.

Address the problem you have identified and quite trying to fix things that don't need fixing.

kevinK
02-09-04, 04:27 PM
I cleaned the throttle body on Sat. The outer surface of the valve is perfectly clean. The inside surface of the valve and the throttle bore has a thick layer of deposit. As I applied carb cleaner, it became sludge, chunks of sludge.

Yes, Bill, there is a hole, which leads to the idle valve. I cleaned that area also.

After cleaning, the gas pedal sticking is gone. The engine idle RPM at gear fluctuates form 575 to 650, and IT DID NOT STALL!

Thank you, Bill. This cleaning saved me a few hundred bucks if I had gone to the dealer.

Although the cleaning solved the stall problem, I am concerned that there is heavy carbon deposit inside the engine. Is there a way to clean it, or is it necessary?

Also, the engine is running a little bit rough with idle IPM range from 575 to 650 rpm. I can feel engine vibrating on the wheel. What could the cause of the fluctuating idle rpm be? There is no code.

Thanks a lot.