E300D surge. Resonance flaps?

[jessie_eaton]

Car: 1997 E-300D, 90,000 miles
symptom: surging (especially around 45-65mph on flat surfaces and not accelerating)

I bought this car about six months ago. My first diesel. I have found no literature to guide me as Mercedes has yet to issue a CD-rom for this car.

Previous posts mentioned a common cause of above symptom. Sticking resonance flaps.

As posts recommended, I cleaned/de-gunked. I wasn't sure what to degunk with so I used carb. cleaner normally used for a gas engine. Hope that wasn't stupid.

When "clean" I reassembled and cranked. Engine ran rough (as expected) and then cleared up. Unfortunately, the surging was just as bad as before cleaning.

I cleaned a total of three "flaps". One located just downstream of the air-filter. The next (following the direction of air-flow) located under a button on the cross-over manifold. And a third that you can see after removing the cross-over manifold.

I did not use a tooth brush to clean, just sprayed it off. I thought that would be good enough.

Is there anyway for me to know if the resonance flaps are operting correctly?

I changed the oil using Shell Rimula Premium (non-synthetic) SAE15W-40 rated CH-4. Not sure what type of oil the previous owner used. Surge got much worse soon after I change the oil. Could this be a contributing factor? Or coincidence?

Thank you guys for this great message board. It has been my only good source of information.

Neil Eaton, PE