99 Grand Am Rough Idle in Drive

I have a 99 Grand Am 4 cyl DOHC, automatic transmission and I have been having a problem with rough idle/vibration while at idle in drive. The second I shift into neutral, park, or reverse the vibration stops. While driving everything seems normal.

I have had the MAP sensor check out, No EGR on the car, a tuneup and transmission service done.

Any ideas on the problem would be helpful!

Thanks ahead of time!

Mary
Phoenix AZ

Welcome to the forum. Have you checked for codes or do you have your check engine light on?


John

We checked for codes but none are showing up on the scanner and the check engine light is off.

Mary
Phoenix AZ

Well sounds like 1 our 3 things to me. 2 have to do with the same thing. I think it could be carb deposits on your throttlebody or IAC casing too much air to enter and a idle surge/causing roughl idle. Your throttlebody attachment screw is misadjusted if you have one or you have a vacuum leak. Could be a great many things but that what I would look into first. Good luck.

John