rough warm starts

[shopower1113]

Recently when I start my car when it is warm the idle is at about 400 to 500 and really rough for about 30 seconds. After the revs come back up to normal the car drives normal. Any ideas what could be causing this. I have a 91 MTX with 90,000 miles. Thanks.

 

[BeatDaSHO]

most likely it is your cam sensor. easy to replace and a cheap part to buy. check your codes. it will probably come up. the same thing happened to me.

Greg

 

[projectSHO89]

I have to disagree with Greg unless more tests are done. Since the engine starts but runs rough, the cam sensor apparently did it's job.

It's easy to test, though. Just unplug the cam sensor. Start the car, it may take several attempts to get it to run as the computer has a 1 in 3 chance of guessing the correct timing on any one attempt. If it starts and runs smoothly, then the cam sensor becomes a more likely solution. (Note: you will loose your TACH when running with the cam sensor unplugged). If it still runs poorly, I would concentrate on two things: 1) Fuel system (pressure leaking down, fuel vaporizing in the rail and running poorly until cool liquid fuel from the tank fills the rail) and 2) the intake system (look for vacuum leaks, possibly the IAB valve).

BTW, how does it perform on cold starts?

Steve

 

[shopower1113]

sorry about the wait to reply(damn work). On cold starts it is fine. Today it was 15 degrees when I started it and the idle was normal.