89, 300E, Rough idle and hard start

Hello,

My 89, 300E was running great. I came to a stop light, and the engine died. I got it started and drove to my mechanic. He changed plugs, fuel filter, oxygen sensor, coolant temp sensor. & coil wire. He says that he put 30 hours into it and still did not fix the problem. He says that he has checked everything he can think of and can't find the problem. The car starts hard but once it starts, it's fine when it's cold. As the car heats up, it starts idleing rough and severely hesitates when accellerating from a stop. My mech says that he though it was the air flow meter, but when replaced, the problem still existed. I tried dry gas, valve cleaner, problem still exists. please advise.

Steve