Odd Ball Cruise Control Issue
 

85 300D 179000

Generally the cruise works pretty well. Lately I've experienced an issue early into my commute drive where I hit cruise and the car keeps accelerating. Doesn't matter if I lock the speed but moving the lever up or down. Manual disengage works correctly. Resume will have it start to accelerate, I hesitate to say "uncontrolled acceleration". After a while, says 10 more mins of driving all is fine and CC works fully correctly. One other thing observed is that while cruising along on cruise, once in a while it cuts out, only for a split second and then it cuts back in. This doesn't happen a lot, maybe twice over 100 miles. I remember doing some CC work on my earlier owned 83's but my understanding of this is the 84/85 have a lot of different ways to control cruise, the tach, the EGR etc. Crappy switch or amp or pickup?
Thanks for any info

Sounds like the "accelerate" switch contact is sticking closed, even though you have moved the lever. We'll see what others think, though...

In the cruise contro switch itself? Maybe I'll yank it and squirt it with some cleaner. In fact, I think I have another one in my basement someplace. Cruise is nice on the long daily drive. Now if I could get some tunes working in the old beast....

I'm still having this problem with my cruise control. For example, if I set the speed at 60 MPH, the car will accelerate to 65 and hold, if I then press down to slow down and release the speed will go up to 70. Pressing inwards releases cruise as does tapping the brake. Seems to be acting up a lot more recently. I've checked all fuses and changed many, tach also isn't working. Cruise will occasioally work as intended but not too often.
Where to begin trouble shooting?

I would lean in the direction of a bad amp. Call Peter at GDL and describe your symptoms....that's your best free diagnosis.

Thanks, I'll do that. I was just at their site earlier today. Handy resource for the amp and ACC thing. I'm going to dump money into this car to get it close to perfect as it is going to be my daily driver for at least 3 more years (except in snow). 100 miles a day, never skips a beat and I'm getting 29 mpg now.

I have a similar problem - sometimes cruise works, sometimes cruise doesn't work, sometimes it sets itself 10% faster than where I set it.

Sixto
87 300D