Question - my E300 runs fine except around 55-60 mph, engine turning 2200-2400 rpm. Under conditions when I have my foot lightly on the accelerator (sort of coasting but not really, not accelerating) the engine kind of bucks and stumbles. If I speed up or slow down a little the problem goes away. It drives great at other speeds and rpms.

I suspect this is the range and speed where the a flap is supposed to open, and it's not opening smoothly, or the computer can't make up its mind to have it open or closed. I don't think the car used to do this though. Could this be the problem?

The vacuum transducers are new, and if a flap goes bad I would expect a CEL - recall the '97s know if a flap is open or closed. Or is there something else that folks have experienced like this that had another cause? Just checking. If it's a flap issue I can live with it, I just worry that it might be something else.

Thanks,

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Charlie

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'66 VW 1300 96K miles
'97 E300D 239K miles
'85 300D 203K miles (sold Sep 2012)

The flap in the crossover pipe is supposed to open at 2550 +/- 100 RPM. Failure of this flap to open will reduce engine torque but should not make the engine stumble and also should set a code, as you have noted. The first owner of my '96 E300 had a situation in which one or another of the flaps stopped working. This set a code and the check engine light came on.

What happens if you drive at 2200-2400 RPM in 3rd or 4th gear (that is, is it the road speed or the engine speed at which the problem occurs)? Stumbling in a gasoline engine at a definite RPM could be caused by either an ignition or a fuel problem but in a diesel it would almost have to be a fuel (IP) problem. A flap problem would reduce the ram air effect of the intake 'tuning,' lowering engine torque but I don't think it would cause stumbling.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
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Thanks for the reply. I'll try driving that RPM on the way to work tomorrow. It happened today on the freeway at about 58 mph and 2400 rpm, but also 52 mph at 2200 or so RPM.

I went thru the whole non-working flap episode last year and can verify that a dead flap does not cause stumbling, but rather just performance that is more sluggish than usual.

I'd agree that it would seem like a fuel injection issue, but what kind of malfunction would act up at a particular RPM, and not lower or higher? I thought about clogged fuel filters, but the car has no trouble doing 75 mph.

Charlie

__________________
Charlie

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'66 VW 1300 96K miles
'97 E300D 239K miles
'85 300D 203K miles (sold Sep 2012)

I had a similar problem with my 1997 E300D .... it would run fine but stumble around 2500 rpm. After messing around with the flaps and all the vacuum control valves in the vicinity of the air cleaner, I eventually discovered that the electric change over valve that is attached to the underside of the intake manifold and controls the two flaps wasn't working right ..... it leaked vacuum. I never quite figured out exactly what caused the stumbling but I knew the change over valve was bad so I replaced it and the problem was no more. I suspect what was happening was that even though the flaps worked and didn't throw any codes the vacuum leak at about the time both flaps were activated pulled too much vacuum away from the other connected systems and probably screwed up the main intake flap control (flap up stream of the EGR) causing the stumbling. At least that is what I suspect. Any case replacing the electric change over valve for about $90 solved the problem entirely. Good Luck.

Thanks, I'll try that. Both transducers over on the right side were replaced last year, but not the controller you are talking about. I'll roll the dice and order one, will follow up here at a later date. I'll also take a look under there for any loose vac hoses etc.

Jeremy, I tried your suggestion and put the car in 3rd gear this morning and yes I got it to stumble at 2300 rpms or so. To me, that points to the acursed flap system.

Thanks,

__________________
Charlie

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'66 VW 1300 96K miles
'97 E300D 239K miles
'85 300D 203K miles (sold Sep 2012)

UPDATE: on the way home from work, CEL came on, code P0120. Here we go again...

Also - in a previous post I said the switchover valve was not replaced previously...checked mechanic records, it was replaced along with both can-style transducers last january. Having said that, one of the parts went bad and I had to take it back soon afterwards - don't recall which part was bad. Everything's been good this spring and summer until just 1-2 weeks ago. Not sure if something went bad again, or leak is somewhere else.

__________________
Charlie

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'66 VW 1300 96K miles
'97 E300D 239K miles
'85 300D 203K miles (sold Sep 2012)

Newbie here...

Any word of what your problem was???

I know I have the exact same problem; even after rebuilt head, IP and injectors... (yeah, long story)

I had the same problem with my 96 E300D.
It's the EGR flapper getting stuck from gunk.
Either bypass it or as my mechanic does is snip it down to make it smaller so it really never closes and continually sucks in fresh air.
The bypass is easy too.
jz

It was the EGR. Search the forum and you'll find the mod where they close up the exhaust side, and put an air filter on the EGR so it can still breathe.

It was an easy mod and what's even better is my mileage went up from 27 to 30 mpg after I did it. What was weird was that for the first month after the mod, the check engine light came on twice, and went off by itself. It's like the intake was still clearing out phlegm or something.

__________________
Charlie

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'66 VW 1300 96K miles
'97 E300D 239K miles
'85 300D 203K miles (sold Sep 2012)