What causes rough idle or stalling on a 1992 Pontiac Grand Prix 3100 V6?

Answer 1

There are a large number of reasons for this condition. I will try to give you a few to check and you can go from there. First, do you have a check engine light on? There are two main issues that cause this...first, lean fuel mixture....second the idle rpm's are controlled electronically so there is an electrical problem. Let's start with the lean fuel mixture. Your engine is getting too much air and not enough fuel to run properly. This can be a large number of things but I would start by looking to make sure all vacuum lines are connected. If you open the hood and hear a sucking sound, then look for that sound. All vacuum lines come from the intake manifold and that is the best place to start looking. If this is to no avail, then it's time to look toward a fuel problem. Basically a lack of fuel will cause you to have too much air as well. This can be dirty fuel injectors, weak fuel pump, faulty fuel pressure regulator or something like that. If I suspected the fuel pressure to be weak, the first place I would look is at the fuel filter and make sure it is not clogged. This isn't the most scientific way to test the fuel filter, but I take it off and blow through it. Tastes awful, but it does provide a good test. If it's difficult to blow through, I replace it. Of course a faulty ignition system can also cause a misfire and not allow the engine to run correctly. Open the hood at night and see if you can see any sparks coming from the spark plug wires to a grounded piece of metal somewhere. If this happens a particular cylinder may not be getting a spark to ignite the fuel mixture. I usually pull the spark plug wires off the spark plugs while it's running to tell me which cylinder is misfiring and then I start looking at the spark quality and fuel delivery to figure out which it is. Computers and Oxygen sensors can also cause this problem but are probably not as likely as some of the other components. Hope this helps Tom