I am experiencing the ever so common high idle problem on my '89 Carat.  Don't hear the infamous hum or buzzing sound coming from the idle stabilizer control valve (how loud is that supposed to be, anyway?), but if I disconnect the wiring harness going to the valve while the engine is running, the idle immediately settles right down to 850 RPM.  If I put the plug back in, the idle speed stays at 850 RPM, no change.  Does this indicate a bad valve, control unit, or both?

Aside from replacing with "known good parts", of which I have none at my disposal, are there tests I can perform with a multimeter to determine functionality?  Can I apply current directly to the valve with the engine off to see if I hear the buzzing?  

Chad Morris
'89 Carat
Salt Lake City