2001 Toyota Camry Engine Idles Rough/Stalls

Engine Performance problem
2001 Toyota Camry 4 cyl Front Wheel Drive Automatic

The problem with my 2001 Camry (80000 mi) is the engine will idle rough and stall out when the car is at a stop in drive. This problem can happen after 10 mi or 200 mi, there is no set pattern to it happening. Sometimes it will not happen for days at a time. The problem can stop after a few stops or after the car is shut off for a few minutes. Also the check engine light stays on all the time. Had it to my local mechanic multiple times but problem was not happening each time. My mechanic runs a computer check but no codes are evident. He resets the codes to reset the check engine light off but can find no problem! The very next time the problem happens the engine light comes back on until I take it back to my mechanic. Problem has happened with 1/4, 1/2, 3/4 and full tanks of gas. There is absolutely no pattern to the problem.