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

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

I should have also asked if the EGR valve could be causing the surge symptoms and how to check the proper opertion of the EGR valve.

NOTE: the EGR valve "exhausts" into the intake manifold between the resonance flap located just downstream of the air-filter and the resonance flap located under the button on the crossover manifold.

Thanks again.

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

Hi,
There was a Dealer Technical Bulletin in 1998 (DTB 04/98)
that talked about this exact problem. I happen to be working on one right now. A 97' that surges and stalls.
On 1997 E300D's the Fuel Injection ecu was modified as a correction. If your Computers part # is 018 545 36 32, there
is a newer version available as a repair. It is #025 545 70 32.
However this unit is very expensive! $1200+.
The next thing that should be checked is EGR. Too much EGR will cause surging at low rpm cruise. Remove the valve and check for
leaks or being blocked open with carbon. The valve should open
fully with vacuum applied and close and seal when released.
The vacuum transducers that control the flaps and egr valve
should be inspected to see if they leak or hold vacuum.

I remember a fly on the wall once told me that a stainless steel
washer with a hole in the center half the size of the egr inlet pipe would reduce pressure that it would tame the wild surging when
installed in the pipe from the manifold to the valve. *****NOTE
***** This would be concidered tampering with federal emissions equipment. Therefore, I cannot condone this type of behavior or
have any knowledge of practices being performed.

Have fun.
DR.DIESEL

P.S. some cetane booster like Red Line 85+ always helps
with running problems on these cars.

Dr. Diesel

Thank you for your information and taking the time to reply. Those are great tips that I did not know about. I will check these things out this weekend and let you know how it goes.

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

Dr. Diesel,

Getting closer, but still have not put my finger on the problem.

I checked the Fuel Injection ecu part number and that looks OK. I also removed the EGR valve and it looked OK (no carbon buildup). The EGR valve opens with vacuum applied and holds vacuum – so the valve itself is OK.

The car runs well when you block / plug the vacuum line going to the EGR valve, but the Check Engine light comes on and the resonance flap located just upstream of the EGR valve (located between the EGR valve and the air filter) defaults to wide open and no longer modulates (will modulate again once the EGR valve has vacuum applied again and you restart the car to clear the error). But again, the car no longer surges when the EGR valve is disabled.

I observed the operation of the EGR system while the car was running. When given throttle, the valve seemed to open with throttle and close at idle as I would expect.

So here is a list of things that may be causing the symptoms:

1) Bad resonance flap or related vacuum controller or related sensor
2) Bad EGR sending unit (located as an intergral part of the EGR valve) giving erroneous signals. This sensor measures the exhaust gas quality and sends a signal to the IFI control module. The IFI control module then determines the recirculated exhaust gas quantity.
3) Some other resonace flap or EGR senor.

My temptation is to buy a new EGR valve (with integral sending unit). Do you think it’s worth the risk of guessing? In other words, do you think this is the most likely culprit?

Also, I think can buy an OBD II scanner for this car. Maybe I should buy a scanner? Or maybe I should just bend over and take it to the dealership. What would you do?

Thanks again for your thoughts and advice.

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

I will be back in the office in a few days.
I can then study your findings.
DR.D