99 ford escort that sputters

I have a 99 escort sedan with a/c that sputters and will sometimes die when you just start the car and put it in gear or anytime that your floor the engine, it also does this when the a/c unit is turned on. Any ideas on what the cause maybe, I brought it to autozone, but they are not getting any codes that are stored in teh computer.

Automatic or manual trans? Does giving it just a little pressure on the accel pedal fix it? If so, try a new IAC (idle air control) valve.