Ok guys I have asked a couple questions about my cruise control but didn't really tackle the problem. I was driving along with the cruise control set on 100 then all of a sudden on a flat bit of road the car accelerated to 120 then dropped back to like 90 then up to 120 again then back to 90 it did this a couple of times so I pressed the brake which deactivated it. then when I went to reset it. It wouldn't set the speed. my guess is that whateva senses the speed is broke so thats why it was changing and now it wont work at all. does this sound rite?? any ideas??
Do you guys know what/where this sensor is.
thanx

Hello,

The way it works is there is a vacuum pump just behind where the window washer tank is it is small and black and should be a small rubber tube connecting the pump to the cruise control unit on the throttle body if this is the problem then my guess it there is a leak of some kind


Widowmaker.

thanx. so nuthin actually senses the speed it is all done by vacuum is that rite??

i beleive so

Your cruise control ecu has inputs from many sensors including Vehicle speed sensor,throttle position sensor etc,etc to control the electric vacuum pump wich operates the throttle valve Take it to a dealer as they are pretty complicated. Could be a number of things. If it was the speed sensor your speedo would'nt work, your auto shift would be erratic and check engine/gearbox light would most likely illuminate.

I have taken it to my dealer and they said it was the brake switch BUT I have tested the switch myself and it works fine and that wouldn't explain what was happening. my magna is a manual too which I dont know if that makes a difference. I might take it back to them and see what they tell me this time. thanx