The idle stabilizer valve may fail, causing engine stalling or excessively high idle speeds.
Car Problem Reports
Volkswagen EuroVan Stalling/High Idle Due to Idle Stabilizer Valve Failure
Volkswagen EuroVan Problem
Visitor, 1993 Volkswagen EuroVan, 104,500 mi
About two years ago and 10,000 miles earlier, when started the engine revved up to several thousand RPM -- completely out of control. The mechanic replaced the Idle Control Valve with a new OEM part, and it ran better but still sometimes the idle was unpredictably higher than normal. Then the computer kept blowing fuse #15 and stalling, so I had to turn up the idle speed to keep from stalling. Recently, I replaced the Oxygen Sensor and Power Steering Pressure Switch with new units, which enabled to computer to work without blowing the fuse, and I had to turn the idle way down. Then a week ago, I lost power on the freeway and was towed to a shop, where they found that the throttle body was clogged ?? and needed cleaning. Running OK, but then the idle speed suddenly jumped way up again, even with the adjustment screw all the way out and plenty of play in the accelerator cable. I replaced the Throttle Body and CO Potentiometer, and the idle speed came way down to 800, but then after a few miles driving it jumped back up to ~3000 and has stayed there. I think the computer is working because Fuse #15 doesn't blow. I guess I'll have to replace the fairly new Idle Control Valve, but I can't imagine it would fail after only about 10K miles. Not likely the Coolant Temp Sensor would be bad, since the problem occurs whether engine is cold or hot.