Gold Lifetime Member
Join Date: Jan 2000
Location: Wilton, Ca. USA
You need to get it to a shop and have them hook a scan tool to it and see what's wrong. It can get expensive just replacing parts. That's the advantage of the computer's; they'll tell you what's wrong (as long as you have the correct tools to read them.
If I had to guess, I'd say change the O2 sensor. Since it runs fine cold and the O2 only is used once it gets up to temp (doesn't use it when cold), it makes sense. If the O2 sensor is bad it affects warm driving only, both idling and cruising (would be worse idling probably).