My money is on either your throttle actuator or a vacuum leak at the intake manifold. It has to be one or the other.

My problem was the same as yours and replaced the mass air sensor, then the throttle actuator, and then gave up and took it to the dealer. They diagnosed a vacuum leak at the intake manifold gasket which solved the problem.

Another user on this site had the exact same problem. He replaced his wiring harness, then the mass air sensor. Same symptoms. He read my post about my problem and asked if I kept the old actuator.

I sold it to him for $300, and it fixed his problem.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".