QuestionWe have a 2000Buick Century with 62,000 Km on it. Starting a year ago it started to stall just now and again. Usually it is damp or raining but has been known to happen on a sunny day but not as often.It will start right away. Sometimes it will just hesitates and not stop. The dealer put it through a diagnostic test wetting everything down and letting the car idle for 2 hours and could not find a problem. It is still under the extended warranty so we would sure like to solve this problem. I am afraid to go out on a rainy day now.
AnswerHello J,
Here are just a couple possibilities.
The mass airflow sensor measures the air going into the engine, and the ECM uses that signal to decide what to do with the fuel, timing, etc.
If that sensor is coated with dust, which they tend to do, the signal is inaccurate, or at least slow.
Here is a link to a discussion about that, and even though it is a Ford link, they act the same on Chevies and Buicks.
http://www.fordscorpio.co.uk/cleanmaf.htm
There is also a idle air control valve that can get dirty and work slowly. It can be cleaned without even removing it usually, although removing it and cleaning it is easy also.
And the EGR valve....it is an item that opens under certain conditions, but should close when you go to idle. They can get dirty, but mainly they will have a tendency to close on a small piece of carbon from the exhaust system, and when they do that, it acts like a vacuum leak. The carbon or rust flake will often be blown out the next time it opens, and all will act normal, till it does it again.
Ask them to check that, and there are screens available to keep those bigger flakes from passing thru.
The EGR valve seats can also just get to where they don't seat as good as new, and do the same thing.
The damp and rainy part almost sounds like moisture related ignition stuff, but the moist air drawn past the MAF sensor could also explain the stalling.
Van
