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Old 04-16-2003, 02:03 PM
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Join Date: May 1999
Location: So. Burlington, VT
Posts: 78
'89 300E cruise control

I just did a search and am confused.........
Here are my symptoms. Cruise control works fine when initially set. If I disengage the cruise by tapping the brake pedal, the throttle sometime (not always) goes whacky. By whacky I mean the engine does not respond to the throttle. The car slows down and eventually heals itself and returns to normal. It can take several seconds or several minutes. If I turn the cruise off, all is fine. I'm reasonably sure the problem is the cruise but after doing a "search" and reading rsults, I'm not sure if the control module is under the hood or behind the kick panel. I'm also not sure if the amp is part of the control unit or separate. Can someone clarify all this for me.
Car is a 1989 300E and perfect except for this anomaly.

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Old 04-16-2003, 02:26 PM
Registered User
Join Date: Jan 2002
Location: Colorado Springs, CO
Posts: 1,006
The cruise control amplifier (also known as cruise amp or amp or cruise control computer) is under the kick panel. They are known to go bad. Tapping the brake pedal should make it go completely off and if it does not, sounds like a SAFETY issue to me. Most often when the cruise amp goes bad it will cause surging or just cut out.

The other parts of the system are the cruise control stalk on the steering column, and the cruise control actuator in the engine bay. The actuator moves the throttle cable based on signals from the computer.

The dealers have a cruise control tester tool. It tests all operations of the cruise control EXCEPT the computer. If the actuator and stalk check out okay, then its assumed the computer is bad.

If your throttle is not responsive, it sounds like the actuator may be hanging up, possibly because of a strangely working computer. I would have it checked sooner than later or stop using the cruise control. Inoperative throttle control is a safety issue, IMHO.
Brian Toscano
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