Can anyone help with a high idle condition on a 1986 camaro 305 engine with a 4bbl carb. The engine idles at 1250 rpm instead of 700 rpm. There is a code in the computer and it is code 24. This points to be a vehicle speed sensor problem. I have removed vehicle speed sensor and bench tested it. It passes the test I get 2 square wave pulses per 1 revolution of speedometer. It says to disregard this code if vehicle is not moving. Well how can the vehicle move if you test the code with the key in the on position and the engine is not running? I am a electrical engineer and It makes no sense to me. I had it diagnosed at the chevy dealer and they said the trouble was in the vss circuit and or wiring. I checked all wiring to and from vss and every thing checks out fine. I have no idea what to check next except maybe the tps sensor. The car has 10,000 original miles and is in mint condition other than it idles to high. Any ideas would be greatly appreciated.

 

The computer is probably assuming that the VSS is bad because you have an open throttle, low vacuum and high RPMs like during cruise, but no VSS signal. That's why it says to disregard if it's not moving, it's an erroneous assumption.

Check the carb first. Is the choke opening? Fast idle cam stuck?