[s-cars] Cruise control debugging

[Wayne Dohnal]

I agree with prior posts that suggested the highest probability cause of 
cruise control problems is the pedal switches, and this was the problem when 
my cruise control quit working.  It would be a waste of time and money to 
replace another component without checking this out first.  I isolated my 
problem by removing the windshield washer resivoir and cruise control vacuum 
pump.  I then "hot wired" the vacuum pump to open the throttle about half 
way.  At this point, if the throttle holds its position over time then it 
might be a control module or other electrical problem.  But most likely the 
throttle position , which you can easily see from up top, will slowly close, 
indicating a vacuum leak.  You can then isolate the leak one component at a 
time, but you may as well start with the pedal switches.  Just plug the 
hoses going to them, run the vacuum pump again, and see if the problem is 
temporarily fixed.

If you don't mind a little micro-surgery, it's not that hard to open up the 
pedal switch and replace the o-ring, which will most likely fix the problem. 
I had a suitable o-ring in my junk collection, but I imagine it's easily 
available at a hardware store.

Wayne Dohnal
1994 S4 



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