Trying to help my friend troubleshoot her car.
Here’s the situation:
The car has been having rough idle (shaking) for about 2 weeks. The car shakes while in drive and braked, but the problem goes away if it is in neutral. At normal driving speed there was no unusual vibration. The car always starts with a lot of hesitation but my friend says it hasn’t failed to start yet.
Two nights ago the CEL came one. The code pulled was P0302, cylinder 2 misfire. I had limited tools last night, and only replaced all the spark plugs. There was heavy white build up/corrosion on the old plugs. I haven’t been able to check the spark plug wire resistance yet and the distributor cap condition. We also put in a bottle of those gas tank fuel injector.
After putting the new plugs in last night, the car was driving fine but the rough idle did not go away. However, this morning the car would stall while decelerating and stopped. This is the first time the car started the stalling problem.
I made a list of possible things to check tonight, but would you fine people please give me an idea where the most likely sources are? I don’t want to start spending money unless it is absolutely necessary. The car is old and a lot of things are overdue to be replaced, but we must prioritize.
IAC valve - since the problem occurs only on idle
Plug wires/ distributor - if that’s are the culprit, wouldn’t that cause problem at all speed?
Fuel injector - I can pull that to clean, but I haven’t done this before.
Fuel filter - If it is clogged, wouldn’t it affect all cylinders?
Check vacuum leak - does that affect specific cylinder? can it affect idle specifically?