I had a similar problem with my '87 300E, that is if I have read the posts correctly!

What happened with mine was I was driving along and then the car would not accelerate. It would creep along but not shut off. Had it towed to a shop and they fixed it under 20$. The accelerator cable wore through a little plastic case and there was no tension. So when the pedal was pressed nothing happened.

Hopefully this can help a little if you still have not found a solution.

Brian