I replaced my multi-function stalk today in an attempt to fix my non working cruise control. The good news is that it does turn on now, but the bad is that it automatically goes wide open throttle. It was quite an eye opener for sure. Seems like a vacuum leak would make it not maintain speed, so what would make it do this?

 

The cruise vacuum servo has two valves to alternately apply and vent vacuum. It may be that the vacuum vent valve is stuck closed or obstructed. The vent side has a redundant valve connected to the brake pedal to mechanically dump vacuum when the brake is applied as a secondary safety. It is also possible that the vacuum supply valve is stuck open.

Another possibility is that the controller is not receiving the VSS information from the buffer box, It could also be that the position sensor (coil) on the servo unit is not sending signal back to the controller module.

 

I did replace the switch above the brake pedal (the one with the vacuum line). That switch should be working since pressing the pedal does disengage the cruise. I also blew air through the check valve and it seems to be working as it should, it only allows air one way.

I may try pulling the cruise module and opening it up to see if there's a bad solder joint in there or something.

 

I removed the cruise module, opened it up, and looked at it under a magnifying glass. I didn't see any obvious solder joints that have come loose. The cable going to the throttle was routed beneath the brake booster which had it in a bind a bit, so I routed it correctly, but still no change.

I can hold the button down (like I'm lowering my set speed) and the throttle will let off, but as soon as I release it, it goes right back to full throttle. My VSS should be functioning correctly since my speedometer works and the torque converter locks up like it should.

edit > I found a YouTube video showing those valves inside the servo. I'll try to pull it off tomorrow and test it.

 

Just an update, I replaced the servo with a used one and it does the same thing. I just received a used module off of eBay that I'm going to try next.

Here's the weird part, they are two different part numbers, however Rock Auto shows them being interchangeable. From my research on G-body forums and elsewhere, it appears GM used different parts even on the same model.

 

Cruise is now fixed! Apparently the modules rarely go bad, but mine did.