I just took my 1991 300E in to have some problems resolved that I haven't been able to fix myself.

The car has 65K on the clock and has been treated with TLC since day one.

Symptom one was a rough idle. The problem was a collapsed motor mount (even though I couldn't tell it).

Symptom two was hard starting in hot weather and occasionally a backfire in the intake manifold. The problem was a leaking fuel injector.

Symptom three was poor gas mileage and spark plugs indicating running rich. The problem was dirty fuel injectors.

BTW, the poorly operating injectors made the O2 sensor test look bad.

I'm having the O2 sensor, the motor mounts and the injectors replaced.

It's going to cost me a lot of money but compared to a new car, it's cheap. Besides, I'll know that it was done right and they gave me a new Benz to drive while they worked on my car.