Cherokee Blues

I'm hopeful that once again someone here might have an answer to my Jeep problems. Since taking over ownership of this 1993 JGC Ltd. 318, I've had the o2 sensor, alternator, fuel pump, IAC and PCM replaced. Most recently was the fuel pump & IAC and it's run fine for about 3-4 weeks. Now this truck is driving me crazy yet again. When driving from cold it's perfect (to the extent a 13 y/o vehicle can be), staying around 800 rpm's. Once it reaches normal operating temp the rpm's won't drop below 1000 - 1100 in drive and 1500 in park. Could it be the o2 again? I'm baffled. I'm watching for the check engine light and it's not setting codes that I'm aware of, haven't checked yet. :banghead:

Looks like the problem may be solved. Took it to my mechanic who, after popping the hood, immediately heard a vacuum leak! :screwy: Still gonna check it all out to be certain.