help! I'm new here so be gentle with me!

My '95 E300D runs, starts, accelerates, and generally runs well at most speeds and conditions. It has decided, however, it doesn't like running(coasting or holding speed) at 2000-2500 rpm. A slight depression of the pedal and it clears up until you let off and try to maintain speed.

it surges and rocks me to sleep. When it acts up, there is also a puff of black smoke after each surge.

A couple of other forums identified a couple of suspect areas such as soot plugged intake, the EGR valve, a vacuum leak or...????

I am new to this particular car, but am a decent wrench, just want to know where to start. Any suggestions?

 

It could be the MAF sensor. Unplug it and see if it still surges.

 

it's diesel.

seems like the exhaust valve is hard to move.

 

Diesels get me every time.

 

ok, somebody tell me what I did. revved the engine sitting in the driveway and saw the culprit causing my surging at 2000 rpm

On the front of the intake tube (right side of car, front of the motor) there is a black plastic vacuum operated servo that (I believe) closes off the air flow under some condition. This is connected by a linkage which goes across the top of the head to the main throttle linkage. ( this looks more like a pull off linkage than an actuating one) At 2000-2500 rpm, this servo cycles the valve from closed to open at about a two second interval, causing excessive smoke (blue). If i disconnect it, power increases and the surging and smoking stops.

Drove it 300 miles today with it disconnected with no seeming negative consequence.

What does the servo/valve do and why? What process is supposed to activate it and why is it hyperactive? What do I need to do?

Where do I get a manual that answers this kind of question on this diesel?

Thanks in advance for the advise and info.

 

it sounds like you are describing an egr valve, can you take a picture of the culprit and surely one of us can identify it.
could be vacume pump baffle problems, etc. let's see a picture.
John

 

I've seen the vacuum transducers for the pressure control flap, and-or the intake resonance flaps go bad and cause surging like you are describing. It seems like they are mounted in the forward right fender area, sort of in front of the air filter housing.

 

I have a 97 E300D, with a lovely surging issue. It use to be only happening at 2500rpm and now its extended the range to 3000rpm. Its really noticeable when using cruse control as it take my foot out of the loop. I can see my resonance flapper near the EGR being hyper even at ideal. I suspect when under acceleration the control flaps are opening just fine. Then when it at steady state at idle or 2500-3000rpm it goes wacked. There are two of these sensors that tell these flaps how to behave. Can somebody please tell me how to check the unit? Is there some sort of test to perform on these units. I dont like shotgunning items when they are $125 a piece. Plus, 1 could be good?
Thanks
Bill

 

Same problem here any answers?

 

That flap works in close unison with the EGR valve. When the EGR opens, that valve closes, and when the EGR closes that valve opens. Both the EGR and the valve that you are referring to are controlled by the EGR relay, and only activate when the engine temperature is over 80C, and at around 2000 RPM or higher.

Some of thew causes could be:
-Stuck valve.
-Vacuum leak.
-A defective EGR relay
-Defective engine temperature sensor.
-Defective Engine wiring harness. (very common on these model)