rbou

Just got this vehicle so I have no history, it is a 87 GTI 16V, 5 speed, with about 150K miles and engine sounds solid BUT, it starts fine and runs right for about 20 or 30 seconds then the RPMs increase to 2500RPMs. The last time I started it ,it started ok but then went to 3000RPMs.I have tested the cold start valve,idle air stabilizer,thermotime switch,all seem ok and I can't find any obvious air leaks.Anyone know any easy solutions? TIA

boschmann

If you clamp off the idle stabilizer valve's large vacuum hose once the engine is warmed up does it affect the idle?

rbou

When I clamp off the hose where it comes off the air cleaner the idle drops by about 300 RPM. When I clamp off the hose near the idle stabilizer the idle does not change. I can reduce the idle by turning the distributor counter-clockwise but then it backfires when I open the throttle. I think the RPM is too high at this point to check the timing. I hope you can help me with this problem as the body on it is in nice shape,with only a cracked windshield, but the interior is rough.I really hate to junk it.Thanks

boschmann

You can't set the timing until the RPM's are down. You checked all the vacuum lines & brake booster line & fuel injector seals for leaks? Pull the air boot off the air flow meter plate & check that it doesn't hit the side or stick/bind. The accelerator cable is not too tight & easily closes against the stop? Does it look like anyone has turned the closed throttle stop, there should be a paint seal to indicate if it has been changed. Remove the idle valve & look into it, the valve should be full open. Connect the harness back & turn on the ignition, the valve should partially close if it's working. Test the coolant temp sensor (it controls the stabilizer valves postition). Resistance should be 2000-3000 Ohms cold, 200-300 Ohms at operating temp. If your car has A/C there should be two idle boost solenoids. Clamp their hoses off to see if one is activated, it wouldw idle down.

rbou

Thanks for the help, you're right on the money! I made most of the recommended checks, when I had the boot off to check the airflow meter plate I noticed the "high speed throttle plate"? was not fully closed. As you suggested I reinspected and found the linkage was corroded, cleaned it up, the throttle plate closed, and seems to idle correctly. Thanks again for the input.