E300TD Ongoing engine fault

clovis57

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I have put several posts on this wonderful and informative site regarding my recently purchased E300TD 98 saloon avant-garde. The fault was and still is:

1. ASR light turning indicating slippery road condition when it is not.
2. ABS BAC turning on ( I’ve been told this can be solved with a new brake light indictor switch that I have ordered one)
3. Increasing speed by its self over 60

The site advised new potentiometer (fly by wire) and the ecu flagged this when my mechanic read it, so a new one was installed all codes cleared, but no luck!

I came back to this site and was advised to take it to MB so they can run there diagnostics, so I did. They found nothing wrong, with a 5 mile test drive as well , no charge as they believed the fault would probably return and if it did, bring it back to them.

The faults were all there again!! So I got a friend to drive it and he immediately said it’s the cruise control taking over …aah, maybe I thought. Knowing that when the ABS and BAC warnings light come on it disables the cruise control this will would be a way of testing’s the cruse controls integrity. The car performed semi normal no self accelerating but would go into 5th when kicking down back into 4th say for overtaking, also I noticed the cruise control kept dropping out when set at a speed. So yes the cruise control is faulty, but why did MB not read this in the ecu? Any way clearly this is the problem for self accelerating as it hunts just like an autopilot system in a plane.

What is the cure for this problem? Isolate by removing a fuse is so how? Or fix the cruise control and how, a new cruise control unit?

The business of not going up a gear when it should a 4500rpm instead of redlining causing the driver to back of the accelerator down to 300rpm when it then goes into top gear. This to me is an independent problem form the CC fault.

Any input would be welcome as with out this problem a great drive.
:idea:
 

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Cant help feeling that this is all speed sensor related, it is not easy to work out.

If the brake light switch was faulty, this would kill the speed signal, not enough maybe to disable the cruise as happens on the earlier cars, but enough to make it inaccurate, the brake light switch is the cheapest and easiest thing to change at £8.75

Change it and take it from there, thats what I would do, this can also effect the gearbox changing gear, other than that I would check the speed signal ring and pick up
 

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