W124 cruise control problems
 

This is on my 87 260E.

I think this might be a common problem...Not sure what part is causing it though.

When CC is engaged, the car accelerates then stops, accelerates and stops within 1-2mph. Its very jerky. Its like the system is hunting for the right speed.... Also, speed up/accelerate works, but decelerate does not. It actually accelerates...

I've heard there is a CC amp under the dash? Could this just need resoldering? Or is there any other parts that could be causing this?

Similar symptoms on my 300SE, except haven't noticed if decelerate does the opposite. Watching this thread with interest......

I'll jump in. Mine started doing that too, '91 300E 2.6. It's one of those things I've been letting go until I get to it. But since the subject is up, I'd love to hear opinions on it as well.

CC amp is under the instrument panel.
CC actuator is under the AFM
Hall sensor is behind the speedo on the instrument cluster.

The system relies on the earthing through the stop light bulbs so if you have earthing problems, bulb problems or wrong wattage bulbs these will have an effect.
The actuator arms may need lubrication. In the worst case scenario the actuating arms could seize causing the actuator motor to short out or a high current to go through the circuit which will burn out your CC amp.
The CC amps - as with other electrical units in the eighties Benzes has a circuit board in it that has been known to develop dry joints ( or cold joints) If you are handy with a soldering iron you can run over the circuit board and re-solder any suss solder connections.

In short many problems with the cruise control.
This is another of those problems where just throwing parts at it may come expensive exercise.

Your Indie dealer should have the appropriate test equipment to sort out problems.

Not really willing to throw money at this car for small problems like this. I'll start with the CC and resolder it. I've had success with resoldering the combination relay before to fix my wiper blades...so maybe that's it.

I've swapped entire instrument clusters (to get a working odo) and the problem persisted, so it can't be the hall sensor.

When you mentioned AFM, do you mean under the throttle plate? Sorry confused on that one.

Where is it under the instrument panel if you have ever removed it? I remember seeing a couple when I pulled it off to do the ignition tumbler on my 300TE.