Cruise aint cruisin
 

Hi, I have a 1987 300E with 142,000 miles on it. I recently purchased the car from a mechanic and he gave me a 1 year warranty on the newly rebuilt transmission. When I am on the freeway and try engage the cruise control the car seems to sort of lurch forward and then back as if the cruise control is catching and then slipping. My question is could this be related to the transmission in anyway so that I can get the work done at no charge. Thanks for any help.

IF you do a search on cruise control you will find tons of information.
The transmission is most likely fine.
99.5% of the time the problem is with the cruise control amplifier.

Again, do a search. TONS of good info.

i agree, it is the cruise control amp.

been there.

cruise control doesn't why?
 

B$ jumping to the amp as the problem, check the tail light bulbs and their connections and the trunk area ground. The cruise control works through that circuit.

I had the exact issue on my 87 300E, yes it was the cruise control amp, it's located under the dash to the left of the steering column, remove the black plastic cover and plug in another used or new cruise control amp and let it hang down while you test drive, if it work properly you then have to remove part of the dash to replace the amp properly, remove the headlight switch, remove the large nut and pop off the panel and that exposed 3 bolts to remove, 2 on the ignition side. If you need more details e mail me and I will help you out but that should solve your problem.

I had the same problem with an 85 380SE. The control module that everyone mentioned was indeed the cause. I resoldered my circuit board and that fixed it. I took an unorthodox approach to removal. I simply bent the metal tangs that hold the board into the can back and slid the board out without removing the whole can. It took less than 2 minutes to get it out and even quicker to put it back in.

Search the forum for "soldered". I have posted tips on this in the past. The real key to the resolder job was burning off the anti-corrosion coating prior to resoldering. I have no idea which solder joint was bad. I did them all.