I've looked at a number of posts on poor idle but have yet to see one that seemed to have the same symptoms I'm having:

The warmed-up idle is about 1100 rpm and it misfires some. On cold start I will get the 3000rpm fast warm up, in response to which I tap the throttle and it will drop to about 1500 rpm and then as it warms up it settles down to 1100 rpm. The interesting part is that after a heat soak (driving for a while then parking it for say 15 min.), I can restart it and it will drop into a nice smooth 700 rpm idle. If I rev it up then it will tend to jump back up to 1100 rpm.

I thought maybe it was the fast idle cam not opening all the way, but pushing the arm down off the rod didn't make any difference.

What does this sound like, some sort of heat-sealing vacuum leak?

Any suggestions on where to start would be appreciated!

 

it's a long shot, but when i bought my car i found it had a lim vacuum leak which caused the car to not idle at all and the previous owner adjusted the cruise control cable to make the car idle. because the cable is not that adjustable, the car would idle at about 1100-1200 rpms and would drop down to 800 or 900 rpms in high heat or when the a/c was running. check and see if your cruise cable is tight all the time. if so, someone may have done the same thing to your car. again, it's a long shot.

 

Another possibility is the throttle cable, which is also adjustable. Luckily this is also easy to check...when it's warm, just feel how taut the throttle cable is in front of the throttle body...see if loosening it has any effect.

 

Thanks for the ideas, but I think the throttle is sitting against the stop (I'll check). Any chance that the idle air control valve likes to stick open, but drops closed when it's hot?