Intermittent, and Runaway Cruise Control -1988 300 SE
 

Good evening everyone.
The cruise control on my '88 300 SE is acting very strange. Usually won't engage. Sometimes it will engage. When it does, sometimes it works great, but usually it seems to make the engine pulsate or accelerate/ decelerate and not really hold constant speed. Also, sometimes after breaking, it won't resume, and cannot be reset. Sometimes after it is engaged and seemingly holding the desired speed ( and this is the spooky part) it accelerates all by itself. What should I check. What would be causing this?
Thanx in advance for your help............

Answer
 

Disconnect the link rod from cruise actuator.

It sounds like the amplifier and actuator are failing = random activation = safety issue..

MB# 0235452132
Fastlane: REBUILT Cruise amplifier
http://catalog.peachparts.com/item.wws?sku=0235452132

MB# 0025458632
Fastlane: REBUILT Cruise Control Actuator
http://catalog.peachparts.com/item.wws?sku=002545863281

Here are some links that may allow you to fix the issue..

Cruise Control Repair Articles
http://www.peachparts.com/shopforum/diesel-discussion/123036-cruise-control-repair-articles.html#post883130

Cruise loves to work...When parked...LOL
http://www.peachparts.com/shopforum/diesel-discussion/137621-cruise-loves-work-when-parked-lol.html



Have a great day.

whunter,
Thank you very much for the quick reply and great info. I'll take heed to your warning and disconnect link rod. I'll also check the web links in your reply.........

I have exactly the same symptoms. My cruise control was flawless before I replaced my heater core. I tried (and failed) to leave my steering wheel in place while I removed the dash. I bent the cruise control stalk in the process such that it wouldn't actuate the switch. I bent the stalk back, and the switch seemed to be OK, but within 10 minutes of using it the first time it starting acting up just as you've described. I've got a switch coming, I'll post my results. (FYI, I didn't go through the troubleshooting process yet, as I'm not comfortable with my old switch and wanted to replace it anyway. So that will be first, getting a good switch installed, then if it continues to act up I'll be more rigorous in my approach.)

my 83 300SD would take off by itself sometimes...from a dead start...i was in a grocery store parking lot and hit the cruise lever while turning the steering wheel and it just took off....scared the ******** out of me...i disconnected the rod

Now THAT is spooky......

Where exactly is this "rod"?

if it's set up like my 420sel then it should be on the passenger side towards the front of the engine mounted above the alternator...look for a long brass rod with little cups on both ends (they'll be snapped onto round things {sorry can't explain better]) you can pop off the rod or just disconnect the electrical harness...the second pic shows where the rod would connect to (onto the ball)

Thanx for the photos, shadetree77. I know the part now, and I'll try the fix.