I have a '99 Legacy Outback on which the cruise control has stopped working.

 

I've already checked the fuses and the switches on the clutch and brake pedals. I also know the actuator is working because I took a length of hose attached to the back of it and sucked on it, which made the throttle move.

 

Here's where things get kinda weird. I attached a vacuum gauge to the line just behind the actuator and fed it in through my window so that I could test it at speed. In activating the cruise control, the vacuum gauge would intermittantly jump up to ~14 pounds before jerking back to 0. It would only do this about half the time. The other half, after resetting the cruise control, there was no reaction from the gauge at all.

 

Since the guage did show vacuum some of the time, I think I can rule out the switches on the steering wheel, but I'm having trouble narrowing it down further. Could it be a faulty actuator pump? Or is it perhaps the control module?

 

The vacuum lines and the linkage to the throttle all seem to be fine, though when I first noticed the problem, I did find the line that goes from the actuator pump to the rest of the system just floating around in the engine bay. (Reconnecting it did not fix the problem.)

 

Any thoughts are appreciated!

I have encountered similar problems in the past with cars, no Subies, but cruise control systems all work the same. Check and re-check the rubber lines and closely examine the actuator for any rubber leaks causing a vacuum leak. When ruling out electrical wiring or switch problems, I could always seem to eventually find a vacuum leak in the system that caused the problem. Some times not easily found, just need to look closely.

Glancing over the lines things seem pretty okay. The actuator seems okay as well, though I could be missing something. Like I said, I was able to move the throttle by sucking on a hose that was attached to the actuator, so that seems to imply to me that it is in working condition.