I have a 2003 Cadillac STS Northstar. My cars idle is real ruff. Almost like a miss fire but theres no check engine light!? Its worse when the car is in gear at idle, and not that bad when in neutral at idle. Almost like a vacuum leak? Has anyone else experienced this? I just put in new spark plugs but still have the problem. help!?!?!

 

i had the same problem with mine and it was because there was carbon buildup on my spark plug wires. give that a check and i hope it works out for you.... unless there is a less expensive fix.

 

Also try checking the Purge Valve. If it is stuck open that will often cause a rough Idle. Also stalling.

 

did u have this problem before u decided to change the spark plugs?