Fast idle when warm - '80 SC

[Danskman]

This problem has kind of crept up on me, and has gotten worse lately with a lot of driving.

A couple months ago, after the car got up to operating temp and was shut down, a subsequent restart with the engine warm would result in a very fast idle; 2,000 - 2,200 RPM. Now, it has started doing this without the restart. After the car reaches operating temp, the idle is really fast. When at a stop light, if I put it in 1st gear and with the brake applied, let the clutch out a bit for just a second (almost simulating a stall), the idle comes back down and stays there (850RPM or so).

Did a search, but couldn't find exactly the same description, so any suggestions? Thanks. It's really bugging me.

[Paulporsche]

There are lots of possibilities for this.

I like to try the easy and cheap stuff first.

Look for vacuum leaks. Does your idle fall when you unscrew the oil filler cap?
Try plugging the top vacuum line to the decel valve.
Check your dist cap and rotor. Make sure the shaft turns and springs back freely.
Try turning down your idle speed.
Your mixture may be off. If you have a gas analyzer, set the CO to 3 to 3.5%.
Your warm control pressure could be off. If you have a fuel pressure gauge check the wcp.
Check popoff valve operation.
Make sure your timing is right and the dist isn't moving.
Check your 15 degree temp switch.
Check O2 sensor.
Check your AAR.
I'm sure there are other things, but this will get you started.


Good luck and let us know what happens.