Cruise control Issue

neverfastenough

neverfastenough

Registered User
Car is a 1995, manual trans. Cruise worked for awhile after I bought it, but one day while on cruise, it applied heavy throttle all of a sudden, around 8psi boost or so and remained there for a few seconds, then the car completely lifted off the gas for the same duration. It went from happening every now and then, to always. Anytime I set the cruise, I immediately feel the pedal pulled from under my foot, and we're off to the races for a few sec!, then it just lifts and coasts for a few sec. Id say if it was set at 70mph, it would pull to 80 as quick as possible, coast to 70, then pull to 80, then coast to 70. Doing long road trips frequently, would love for it to work properly. Any ideas?
 
neverfastenough said:
Car is a 1995, manual trans. Cruise worked for awhile after I bought it, but one day while on cruise, it applied heavy throttle all of a sudden, around 8psi boost or so and remained there for a few seconds, then the car completely lifted off the gas for the same duration. It went from happening every now and then, to always. Anytime I set the cruise, I immediately feel the pedal pulled from under my foot, and we're off to the races for a few sec!, then it just lifts and coasts for a few sec. Id say if it was set at 70mph, it would pull to 80 as quick as possible, coast to 70, then pull to 80, then coast to 70. Doing long road trips frequently, would love for it to work properly. Any ideas?
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I don't know if the switch has anything to do with it, but there is a switch on the top side of the brake pedal that has a yellow button and black housing that can slide back and forth. I learned this recently doing my teves, I pulled back on the brake pedal and hear clicking and it was the switch "ratcheting" back. I would try to adjust it down towards the brake pedal arm a click or two, maybe its losing its contact after initial set?

There is also the pump and some other stuff behind the inner fender well by the corner light but I don't know quite how all of it works.

John
 
I dont know. Guess I would maybe clean all electrical connections first. Thats not gna be fun.:(
 
My Dad had a 1981 Buick Riviera FWD v8 that did the same thing. It turned out to be a cruise sensor on the throttle linkage. Obviously not the same car, but worth noting.
 
Bringing this back up for some more eyes to see, I havent done any diagnosing. 14hr trip tomorrow in the car, cruise would be awesome.

Again, the problem: set cruise and car goes nearly WOT for about 2-3 sec, then completly closes the throttle for 2-3 sec, then goes back wot for 2-3 sec, and repeat and repeat and repead until I kill the cruise.

hoping someone has had this and its a simple fix. 95 5spd car
 
It might be worth checking switches in steering wheel. Maybe wires shorted, moonroof leak or soft drink spill. Liquid in a switch can make them do strange stuff. Might even be a stuck accel or resume wheel switch and out of adjustment breaklight switch.
Just some ideas.....good luck
 
scskydivin said:
My Dad had a 1981 Buick Riviera FWD v8 that did the same thing. It turned out to be a cruise sensor on the throttle linkage. Obviously not the same car, but worth noting.
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That is more likely.
The SC does not have a full electronic cruise control.
I think it might be a vacuum leak either in servo itself or in the vacuum line going to/ from it.
It seems that the servo is being commanded to hold a given speed but while the setting stays the speed is drifting until you it the max tolerance, then the servo is being repositioned to resume the set speed.
I will post a picture tonight
 
similar cruise problem

I have had a similar problem with an 89. The car accelerated and coasted around the cruise setpoint, although it never did approach WOT like your problem. You could watch the vacuum gauge cycle towards boost and back. I have always suspected a vacuum leak, and although I found and rectified a few, it kept doing it until recently it quit working at all. It now feels like the car is trying to maintain speed, but any type of incline and the speed steadily decreases. I am hoping to get some time to work on this in the next week or so. WIll post up if I find the problem.

Horn
 
Cruise control issue

Good evening

Have you checked the Vacuum Dump Valve? There could be a leak at the valve and or the valve needs to be adjusted to allow no vacuum leaks.
 
when mine did this inside the fender on the big round vacuum diaphram i forget what its called it has a small plug or vacuum bleed it was missing that little black plug that covered the small hole so it was basicly a vacuum leak
 
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Heh heh, mine hasn't worked since I bought my SC in about February of this year. Now I don't feel so bad that these are known to go at some point.
 
yea i think you can see the plug on the first picture on the left on the back side it is hard plastic a picture from the back might show it better
 
no obvious vacuum line probelms

Thanks for the pointers everyone. I pulled the front wheel off today and the splash guard to access the servo. Found all vacuum lines were made and no missing plugs. Adjusted the cable on the throttle body, but it wasn't really loose. Dump valve on back of brake pedal is adjusted within spec according to manual. Took it for a test drive and noticed that if I am applying pressure to the accel pedal, I can depress the SET/ACCEL tab on the steering wheel and it will try to hold that speed. As soon as I let off the tab you can feel the car start to decelerate, just like you've pressed the "OFF" button for the cruise. Drug out a shop manual for a 1990 (the car is an 89) and there is a KOEO/KOER set of tests to run, but ran out of time. Going to try that tomorrow. Any progress w/your car, neverfastenough?



While tracing lines, I found this vac connection/sensor(see circled item in the pic). The narrow vac line (arrow) running across the top of the clutch reservoir is plugged off, top vac hose runs to a vac juction block, electrical sensor goes? I looked at two other birds (both of which cruise works, neither an 89) and neither one of them had this particular item. Don't think it's related to this issue, but anyone know what it is?

Horn

sccoa vacuum.jpg
 
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Well I got rid of the car so I didn't get a chance to fix it on that. However I replaced it with a 95 cougar that did the exact same thing :mad:. Cleaned the contacts on the cruise control amplifier and problem solved
 
neverfastenough said:
Well I got rid of the car so I didn't get a chance to fix it on that. However I replaced it with a 95 cougar that did the exact same thing :mad:. Cleaned the contacts on the cruise control amplifier and problem solved
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Where is this amplifier and what does it look like? same problem with my five speed if i keep light pressure on the throttle it wont do it its wierd
 
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