I have a 1982 380 SEL. I have a fast idle problem. The engine runs fine and most of the time idles around 500 RPMs. However for no apparent reason, the idle will suddenly rise to 1500 to 2000 rpms. Then after a while it will drop back down to 500 then go back up after a few minutes.

I tried to kick down the trottle, no change. The thermostat has been changed, no change. I don't think its a throttle linkage problem as the idle will increase even when I don't touch the accelerator.

Any suggestions?

Thanks,
Brad.