I have read several posts on this but have not found help.
Basically my daughter's 79 is idling about 1800 when cold and hot.
I recently replaced the CHTS, the wiring harness attached to the CHTS, the plugs, the thermostat and air filter. I'm pretty sure there is NO vacuum leak. I replaced all the vac lines.
What to check?

 

Supposing that ALL sensors are working correctly, I would check the TB stop screw. There's also a huge idle adjustment screw.

 

Just to close this thread I should add the problem was the plenum wasn't installed properly at the throttle body and air was getting past.

 

That would be the OTHER throttle body adjust screw - the one that holds it onto the plenum lol