I agree with you.
I've read dozens and dozens of cases like yours on this site, and not once has the cure been to replace the ECU.
Based upon the common fixes that you usually read similar to your problem, I'd say it could be a vacuum leak (from a hose or the intake manifold seal), the idle control unit, but my best guess would be the mass air flow meter.
If you have a gauge you can check to see if you have low vacuum. For the intake manifold seal, you can spray water around the gasket and see if you have a leak.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".