99 Grand Am rough idle when warm

[RRWarren]

Have an automatic 99 Pontiac Grand Am. Recently had my water pump and timing chain tensioner replaced. Now when the car is WARMED up, and at IDLE, it get an engine vibration that transmits through the brakes. Engine vibration increases the longer it sits. When RPM's increase, it stops. Vibration not related to vehicle speed. Oil and coolant levels are good.

[GTP Dad]

Welcome to AF!

You may want to remove and clean the idle air control motor from the side of the throttle body. Also if you have a lot of miles on the car clean the throttle body itself. This should help with the idle situation. Use throttle body cleaner to do both.

[DGHIBNER63]

I had the same problem with my grand am. When they replaced your tensioner, did they also replace the low idle sensor or controller? We had that done when they replaced our timing belt or chain and it cured our low idle problem. My first thought is that the sensor or controller is located at the transmission or in it, but I don't remember for sure since I am almost certain the timing chain is on the other end of the motor. Let me think if I can confuse this issue more...... nope. Sorry, but maybe there is someone who can expound on this and clarify. It was just too long ago. I remember it was an expensive fix and was pretty sure it was tranny related. Just a sensor or control. I think we had the timing chain replaced since they had to remove the cover to replace a bad gasket. I really hope this helps.

[3100]

I would remove serpentine belt for a moment and start the engine see if vibrations stop. At least you will know that it is not torque converter, trans or engine chain related. It could be one of the pulley's bearings.

When you remove serpentine belt with engine off of course try to spin each pulley and listen for unusual noises, then try to move pulleys left and right up and down looking for any movement. Also before you remove the belt look at each pulley including alternator's pulley for jumping movement while engine is idling. I had problem once with alternator pulley which was transmiting vibrations only through accelerator pedal at certain rpm's.

[Chuckoly9]

Check engine mounts for collapsed or grounding out or loose mounting bolts.
timing chain repairs often require mount removal to gain access. if mounts are in abind, loose, collapsed, or metal part of mount grounded out to body or frame this could be the source of your vibration/roughness