I own a 1990 300D 2.5 turbo diesel (chassis 124.128), and I am experiencing an odd acceleration problem. The acceleration is sluggish - especially when trying to go from 40 to 60 mph. It feels much like it does if the vacuum line has come off the turbo (except without the transmission jolts you get with a vacuum line open to the air). But here's the catch: turn on the cruise control and the problem goes away.

The problem is most pronounced when trying to accelerate on an a slight uphill above 40mph. In that situation, when I nearly floor the pedal, the transmission will downshift, and the car will struggle to gain speed. If I then turn on the cruise without moving my foot on the pedal, the car will jump back into fourth and accelerate quickly.

The gas pedal linkage appears to be functioning properly (at least it moves through its proper full motion when I'm parked at home), so it does not seem to be a case of the cruise being able to push the linkage farther than the pedal does.

Any ideas?

My guess is that your turbo is cutting boost.

Grab a 12 pack, get comfy, and read through this thread...


Wastegate actuator swap for OM602.962?

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93 300D 2.5 Turbo, Black/Palomino 273K
09 E350 Black/Black 41K

Any Excuse: ( 'Wrong Moon Phase,drop in ambient Vacuum on Alpha Centuri,
Your mother in law is on her way,Etc,Etc,Etc.) and the EDS [Computer] will
deny you "BOOST".

The GSXR Crapola Removal System is the way to Go.
Once installed, the ONLY thing the EDS controls is Idle Speed...
AND it cannot deny you a "Nice , Smooth" idle No matter What !

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'84 300SD sold
124.128

I third what they said.

It did seem quite daunting at first but once I got my mind around it, it was very straightforward and I had BOOOOOST aferward.

My transmission also magically started shifting the way a Mercedes is supposed to shift once I eliminated all the real and potential vacuum leaks in the "rat's nest."

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1993 W124 300D
-297K on the clock as I type this.

Thats funny you say that about your tranny. Mine shifted MUCH better when I removed the rats nest as well.

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93 300D 2.5 Turbo, Black/Palomino 273K
09 E350 Black/Black 41K

On a similar note, is the AFM required for the EDS to control idle speed or is there a work-around (trying to simplify the air-intake system).

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Gone to the dark side

- Jeff

Thanks much for the replies. Removing "the rats nest" and going cleanly mechanical seems rather daunting to me. I think I'd rather make the thing work if I can - except that I have no idea what the cause is, and it sounds like I'd have go digging around Alpha Centari to find out.

AFM isn't used for idle. Only for EGR, ARV and those intake flaps all over 90s engines.

Sixto
87 300D

nmagner,

'Nah ! took me maybe 35 minutes to remove all of it!(That's the easy part)

The Pressure Operated Wastegate modification is only slightly more complicated.
AND "Blocking" and removing the EGR ain't hard.

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'84 300SD sold
124.128

I agree.

It's not that hard once you think it through and get it all sorted out in your mind.

It's also much less expensive than replacing all that crap because they don't work anymore.

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1993 W124 300D
-297K on the clock as I type this.

Get your self a mighty vac. Check for the obvious, Loose hoses, cracks, bad connections. Also you can pull codes from the computer with a multi-meter (analog) Count needle swings. It might give you an idea where to look.

I you have any other questions don't be afraid to ask.
Bob

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92 300D 2.5L OM602 OBK #59