Drove down to the store today, we live in a rural area and there is a good stretch of straight, safe road and I opened here up, got to a corner, let off the accelerator and she kept going.....

Put the clutch in and used the brakes to come to a stop while the engine red lined..........shut her down..

Assumed the throttle cable or linkage stuck, perhaps the gas pedal got stuck against the carpet etc etc.........

Got her home and checked every single linkage, connection etc......

Disconnected the small linkage on the gas pedal near the floor at the firewall, not the cable but the "ball and socket" linkage, am I correct that this is the "cruise control" linkage?

When I disconnected this linkage she idled, revved and returned to idle fine........ I have come to the conclusion the cruise control is screwed up and when I hit the throttle the cruise control took over and stayed there?

What is the best, safest and permanent way to disconnect the cruise control, I have never used it.........thanks for any input, need to go change my shorts now.....

 

If it does not interfere with any accelerator/linkages movement, and you are sure this caused the issue, I would simply leave the cable disconnected for the time being. You can then sort out the issue at your leisure if you are so inclined.

 

It is running fine now with the small "ball and cup" linkage disconnected at the gas pedal, there is no "cable" as such, just the short plastic and metal rod.......I think I will see if I can remove the entire linkage to avoid anything catching........I have never used cruise control and never will, don't trust it. I thought about removing the fuse but other systems that I need are on the same circuit so that is not a choice, thanks.

 

Or remove and plug the vacuum line leading to the servo above the pedal. That or the linkage off will render the system inoperative.
I'd reconnect the linkage so it's not flopping around down there as the plugged hose would be easier to tie wrap to something.

Is it "off" on the turn signal stalk ??

And you didn't turn it on or use it ?? It just engaged itself ??

 

Good suggestion about getting rid of the linkage completely...

The cruise control switch on the turn signal arm was off, never has been on, that is what totally surprised me, I thought the system would need to be "energized" even to malfunction...?

Another reason I want to totally disable it.........

 

Yup, if it's off it shouldn't be getting any power to operate and once you pushed the brake and clutch as they each have a cut off switch the system should have disengaged.

That's three separate things that needed to fail to allow this to happen.

 

My thinking is, part of the gas pedal operation is controlled by a linkage connected to the cruise control system that is vacuum activated right? All it would take is a vacuum source to move the linkage and "accelerate" the gas pedal...or at the very least, keep the gas pedal accelerated to where I had it.....

 

I haven't been inside one of the cruise control main units. Everything in any cruise control system is designed so if there is a failure the system doesn't work . . . but ???

 

The cruise module under the battery tray should have a vacuum line and plug on that pump. You can disconnect both of them as well.

 

Someone with alldata should see if there's a tsb/recall for this.

 

Call me crazy, but I have a question. Are you absolutely SURE it is the cruise control causing the issue? With the cruise linkage disconnected (and the engine off) have you floored the accelerator several times to be sure the linkage is not hanging up? I just want to be sure you have completely eliminated the regular linkage system, a sticking throttle body butterfly or anything else. I don't want you to get a big surprise again in the future. You know, with all of the fail-safe's in the cruise system, it baffles me how this could have happened. Not saying that it didn't, just baffles me how it did!

 

Good morning, I spent the day going through everything yesterday, with the cruise control linkage disconnected at the gas pedal the car runs and drives fine, "floored" it a number of times and the normal throttle linkage is working 100%...........

I hooked the cruise control back up, with the car parked but running, increased engine speed and when releasing the gas pedal it stayed where it was, there was tension on the small linkage from what I assume is the cruise control booster unit just under the dash?

What it seems like to me is this "booster" unit is always "charged" and wanting to advance the throttle???

I do not know how the cruise control system works but plan on doing a lot of reading and research to find out, even though I plan to never re-install it or use it, just would be nice to know what the hell is going on......

I understand there are a number fail-safe's in the system but the system was never turned on at the turn signal lever, this is what confuses me..??? It just appears there is constant pressure at the small linkage arm at the gas pedal...? Seems like it is getting vacuum pressure all the time at the "booster"..???

I will do some more testing, reading etc and let you know what I find, thanks for the input.

 

It's a strange linkage, mechanically, compared to every other car I've ever owned. It certainly should not "always be charged." Quite the opposite on every car I've had, but I admit volvos are strange.

So it sounds like in your case it could be sticking, or else a vacuum valve is leaking through. I'm sure you'll figure it out. Since you don't use it, I supposed disconnected is the way to go.

As you can see in the digram posted on page 1, there are two dump valves, one on the brake pedal and one for the clutch pedal. If you think it has vacuum on it, then you should try dumping that vacuum by stepping on the brake. If that doesn't work, then vacuum is not your problem. You've just got something mechanically sticky.

 

I don't believe it works like that. My understanding is the brake and clutch "solenoids" are electrical and send a signal to the main cruise control "modulator"...? In other words, when you hit the brake or clutch it tells the "brain" to shut off the vacuum......... the vacuum is supplied to the booster to actuate the gas pedal, that is controlled by the modulator/ actuator???? Still researching the whole thing but it is starting to make sense as to how this happened.......... :-)

 

From the diagram I posted those controls on the brake and clutch assemblies are vacuum valves, not electric. Not sure if that diagram is exact to your year. It was a diagram for my '95 850.

I know in most cars those controls are switches and they trip the main cruise control assembly into turning off.

 

My vehicle is a 1997 850 as per my signature.. ;-)

I am looking into the cruise control system, I do know some of it is vacuum controlled and some electrical, just figuring out what is what, bottom line, something went wrong and it will be nice to know what it was, thanks for your input. :-)

 

I was with you. I am used to them being electrical so it was a bit of a surprise to see they were vacuum on mine. I don't have a diagram on a '97 so I wanted to point that out since they might change something between mine ('95) and the one in your signature. The chances are good thought it's the same system with the same components.
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They are a vacuum switch but it sure looks like there is an electrical connector on it too. I use mine all the time and haven't had any problems with mine so I haven't worked on it and I'm not familiar with it like some other things on the car.
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