Idle problems

I have a 1993 Camry with a 3.0 V6 engine. I have been having problems with my idle for the last two months. Originally, the idle would drop down to about 400 when I would slow to a stop and then jump back to normal after about 10 seconds. My mechanic said to change the IAC valve which I did (with a salvage yard part).

Now with the new IAC valve, here's what's happening:

The idle works fine when the engine is cool. Once the engine warms up, it idles at about 400 consistantly regardless of whether I am in park or drive with the brake engaged. While it's idling this low, the car vibrates.

If I turn on the AC, the idle jumps to about normal and fluctuates between 850-1000. While fluctuating, the engine sounds like it's revving itself repeatedly. Once and a while, even with the AC on, the idle will drop down to 400 and the car will shake pretty badly.

The biggest problem with all of this is that I'm supposed to drive to Key West from New Jersey this weekend so I don't have much time. If the problem doesn't get any worse I'll still take the car since it's mostly highway driving anyway.

Did you clean the IAC valve before you put it in?

Did you clean the IAC valve before you put it in?

As far as I know, it was clean already when they put it in.

You might want to check that, check the EGR valve & check for vacuum leaks.