I have a 1998 Lumina 3.1 with about 170,000 miles. This car idles correctly ONLY under these circumstances:

1. In any gear EXCEPT park and neutral. It idles smoothly in drive & reverse no matter how long idling in gear
2. In any gear INCLUDING park and neutral with the A/C turned ON
3. Before the engine warms up

As the engine begins to warm (in park or neutral) the rpms begin to lope eventually ranging from about 500 - 2000 rpm. If I turn on the A/C it returns to a smooth idle. If I put it in gear when it is hunting it will also return to a smooth idle regardless of the A/C setting. In other words, if I have it in gear or have the A/C on it always idles fine. If I am sitting in park or neutral with the A/C off it begins loping till it eventually dies on the down swing.

It seems like I would be lots more likely to be having this sort of problem with the air on or idling in gear not the other way around.

Anyway, if anyone has had this problem or has any ideas I would greatly appreciate their assistance.

Thanks, Pat