My '97 E300D surges and the tachometer ossilates up and down. I cleaned the resonance flaps with carb. cleaner normally used for a gas engine. Hope that was ok. Anyway, the resonance flaps are clean and problem persists.

Next, I disconnected the vacuum to the EGR valve to disable the valve. The car ran GREAT.

But with the EGR valve disabled, I noticed that the computer tells one of the resonance flappers (the one located between the EGR valve and the inlet air filter) to default to wide open and the check engine light comes on.

I checked the operation of the EGR valve with a vacuum pump. The valve works fine. Maybe it's the EGR sender?

Any thoughts?

__________________
Neil
1997 E300D - naturally aspirated
280,000 miles (as of November 2015)