M104 2.8 HFM hesitating/rpm down and up while coming to a stop - Page 6 - Mercedes-Benz Forum
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post #51 of 57 (permalink) Old 08-27-2015, 08:34 AM
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Despite new ETA ( throttle body) the symptom show the problems origin from the potentionmeters , at a same time could be ASR involvement also. ( this idea jump in my mind, because you wrote ....."slowly braking more then sometimes the RPM goes down to 250/300 or so and the car shudders. ...")
We have to detailed clarify, how the ASR really work, what kind of command goes when and where from ... You mentioned earlier, has been changed the CTP switch also ( it is for ASR only) Maybe there some connection problem, or the new S29/3 CTP switch still not OK, or not properly installed, adjusted? who know?
After all it is suspecting for me, the shuddering related with brake, this not happened with my (w/o ASR) ETA problem, on the contrary , potentionmeter problem causing irregular idle and grabbing during acceleration.
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post #52 of 57 (permalink) Old 08-27-2015, 09:18 PM
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Just A Guess

Does the brake master cylinder draw vacuum? Could you have a vacuum leak, possibly at the transmission? As the vehicle slows to a crawl, foot on the brake pedal, could a vacuum leak drop the idle like that?

Is there anything in the emissions system that might cause this drop in RPM? EGR malfunction? Drawing a vacuum on the EGR valve will cause the RPM to stumble, correct? Isn't that the test of an EGR valve?


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post #53 of 57 (permalink) Old 08-28-2015, 01:02 AM Thread Starter
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@pbuchmueller66
Thanks for your reply! I still don't think it's the ISC/CC. You could of course be right but I'd be really unlucky.
I do not have ASR so that is out of the question.

Also the cruise control works perfectly. I've tested this a few times.


@LogicalPosition
Thanks for your reply too!

You might be onto something here with these vacuum leaks. I think I'm a bit of a newbie with the vacuum system so I would need some help there how to diagnose this
As my brakes are not the best I have done several things to improve the braking (front brake pads + lube, rear brake pads and new brake hoses + brake fluid this weekend). It's still not very good but as part of diagnosing the brakes I have done a test which the guys on the Dutch w124 forum told me: With the engine off, step on the break a few times until the pedal feels hard, start the engine and check if the pedal goes down, which it did. Would that be significant enough of a test or do I need to check some vacuum lines? If I do, how do I check them spray something or?

I do not have a EGR valve or a smog pump, maybe that's the positive side of having a euro spec M104

Also, not sure if this is important but I'd thought I'd just say it anyway. When I bought the car the gas pedal felt weird. The first bit when you press it felt loose/soft and then it would give a lot of gas. Some guy from the Dutch forum adjusted the cable when I was at his garage getting some second hand 8 holer rims. Later I tried adjusting it a bit myself according to some workshop manual, it felt much better but I'm not sure if this can have any impact on my problem.

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post #54 of 57 (permalink) Old 08-28-2015, 03:21 PM
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There is only one line that supplies vacuum to the brake booster. It becomes brittle with age. In the middle of that line is a check valve. Check it closely, if it gives way, you'll have manual braking...not good to discover while you're under way.
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post #55 of 57 (permalink) Old 08-28-2015, 03:45 PM
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[QUOTE=Gripen;12802521] @pbuchmueller66
Thanks for your reply! I still don't think it's the ISC/CC. You could of course be right but I'd be really unlucky.
I do not have ASR so that is out of the question.

Also the cruise control works perfectly. I've tested this a few times.




in the ETA are 2 potentionmeter. One is for the idle, other could be serving the cruise control. Several other case, wiring OK, but the customer complained about idle we replaced the throttle body immediately - job done, problem solved. Glaube mir, pot-meters sind Verschlei▀teile, und nicht reparierbar.
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post #56 of 57 (permalink) Old 08-28-2015, 03:58 PM
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ahhhhh, talking about pot meters something jumped in my mind: you mentioned throttle-body has been replaced earlier - the linkage also realignment properly?
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post #57 of 57 (permalink) Old 08-29-2015, 03:50 PM
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CC/ISC trouble check 14 pin banan plug test OBDI codes
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