QuestionQUESTION: I have a 1990 volvo 740 gl. The problem it is having is when I start it to let it warm up, it skips and sometimes stalls out. Then when I am driving it, and come to a stop at idle speed it will do the same thing..skipping/stall. The problem is intermittent, sometimes happens, sometimes not. Check engine light went on 2 weeks ago, and codes came up Idle Air Control motor, and knock sensor. I replaced IAC motor, problem is still there. I am really stumped, could this be a relay problem, a air flow/sensor problem, etc...Any thought would be appreciated.
ANSWER: Chris,
Well what you do not know is wheather the cause is fuel. I would hook up a fuel pressure gauge and drive to see if the problem is lack of fuel. The fuel pump or the relay will not set any codes, so you could take a chance and change the relay especially if it is old, or original.
---------- FOLLOW-UP ----------
QUESTION: Thank you for that info Ray. I was doing some more poking around on the internet today, and found some that said perhaps the problem could be something with the ignition coil, or electrical part of ignition switch, or even a bad spark plug. Do you think any of these ideas have any merit?
AnswerChris,
Bad spark plug yes, that would cause a mis-fire. The electrical portion of the ignition switch I doubt. Coil maybe, but they are not to prone to problems. When you start the car up cold have the hood open and with care and caution as the engine just starts to run gently touch the exhaust manifold to see if one header is cold or cool as the others are hotter. That would mean that the cooler cylinder is not firing and that is the one you need more inspection on. You only have a few minutes to do this quick test. Then look at the plug take a compression test, replace that wire and plug.
