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Rough acceleration

1K views 7 replies 3 participants last post by  Rickysa 
#1 ·
I've tried to do my homework before posting (google, search here, search mercedesshop, read over the CD manual) but I haven't found an answer to what must be a common question.

Smooth idle, then very rough acceleration from stop thru first gear only, then smooth again.

I suspect an air/vacuum issue as I've just finished replacing the defrost vacuum element and the changeover valve, and everything was running great before so maybe I've dislodged something while troubleshooting the climate control issues???

I've got the vacuum diagrams for the climate control, but cannot find any other vacuum diagram on this CD (from mercedesmanuals.com)

As always, any help is most appreciated.:)

Rick
 
#2 ·
With a 103 I say cover the basics first: what PM have you done? Cap/rotor/plugs/wires? 103s are fussy about that stuff. How many miles? How old is the fuel pump and filter? A new fuel pump/filter fixed my SE when it was doing this.

Yes, check all the vacuum fittings, it may be something not related to your recent fix.
 
#3 ·
Thanks for the reply...

I've just recently taken ownership of the car and am working thru the already present problems...monovalve, full-time defrost, radio replacement, etc and when I took it out for the "it's done!" drive, I noticed the acceleration problem.

In reading the previous threads dealing with rough idle, it seemed to be consensous to replace plugs/wires/etc.....but since my idle is smooth and acceleration past 1st is smooth, I was thinking vacuum...just not sure where to look.

Rick
 
#4 ·
You may have a vacuum or air leak but this generally results in a high idle or rough idle. Under throttle the air and vacuum pressures equalize and the symptoms go away, to return again at a stoplight, for example.

(I’ve been through the hell, I know…) :(

Vacuum problems may also effect how the transmission shifts but again not effect engine performance under throttle.

In your first post you state: “Smooth idle, then very rough acceleration from stop thru first gear only, then smooth again.” It seems your tranny is otherwise shifting correctly and the engine is stumbling off the line.

If you have no history on the car you need to replace the cap/rotor/plugs and perhaps the wires anyway. If the car is over 100,000 miles a new pump and filter would also be in order.

You can check the fuel pressure performance to test the pump if you like, that would turn up a fuel delivery problem. Next would be to check the MAS control unit.
 
#6 ·
If you have no history on the car you need to replace the cap/rotor/plugs and perhaps the wires anyway. If the car is over 100,000 miles a new pump and filter would also be in order.

You can check the fuel pressure performance to test the pump if you like, that would turn up a fuel delivery problem. Next would be to check the MAS control unit.

Will do, and thanks for the summary on how vacuum issues would effect the performance...I was hoping the symptoms I was presenting would include/exclude some troubleshooting avenues. MAS and fuel pressure to be checked tonight, and other parts ordered just now.

Many thanks:thumbsup:

Rick
 
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