GMC Repair: rough when idle - sometimes, auto part store, oxygen sensor


Question
hi i am hoping you can help mw as my problem does bot seem 'brand' specifuc. thanks for your help.
1- 98 Avalon, 95K miles
2- steady tack, but rough feel - 1/2 the time - when stopped and in gear. Seems related to outside temp.
3- throttle body clean, air cleaner clean.
4- orginal wires - runs same when raining.
5- original everything, plugs, fuel filter.
6- needed to replace ignition coil last year - Autozone part (regretfully)
7- no codes read by amatuer mechanic at work.
8- Timing belt changed early in november.
Its far from horrid - but of course would like it 100% as it was.
Thanks, Mark.

Answer
there are a few things the idle could be. It could be the:

Idle control valve
MAP (manifold absolute pressure) sensor.
O2 sensor
Temp sensor
Idle speed control.

Next thing you should definitely replace the plugs, wire, fuel filter, and oxygen sensor. typically, a tune up consisting of the above and a few other things, should be done every 10K miles. Or by manufacture specs. Autozone, regretfully?

 I would try the tune up first. Then look at the idle control if that does not fix the problem. I would strongly recommend adding a bottle of Lucas every other oil change as well. I will recommend that you add one container, available at any auto part store or mass retailer.

 If this does not fix the problem(s), email me: marvin.saunders69@yahoo.com