Quote Originally Posted by Ron View Post
While the engine is warm, pull "the hose in the middle" off and see if it has vacuum on it. It should (RPM high or low). If not, check that the other hose has vacuum and swap them. (This allows the vacuum to vent when the solenoid disconnects the vacuum from the distributor. Otherwise, once you rev it, it can have vacuum to the distributor until you shut the engine off...)

That is the way it should act whenever the throttle plates are shut (idling). (The wire to the solenoid is always hot -- The switch grounds the solenoid to close the valve and vent.)
When the throttle plates are closed, the switch should turn the idle system on and the vacuum to the distributor advance off. When the plates are open, the idle system is deactivated and, if the engine is warm, vacuum is applied to the solenoid -> distributor. (If cold the Thermal Control Valve routs vacuum to the Warm Up Regulator instead of the solenoid -> distributor). Rather than pull "the hose in the middle", pull the other hose and check that there is no vacuum on its solenoid port when the plates are closed (idling, warm).

Although you replaced the mode switch recently, there is something wrong there. Moving the mode switch to cooling modes should not affect the engine RPM except for the AC compressor adding a load (the idle system should basically compensate for that). No way would a good AC system pull the RPM down 500-700 RPM. Double check ALL of your vacuum routing.

You may have bad springs, but that wouldn't cause the mode switch to affect the RPMs.

Again, you can plug the main vacuum tap to eliminate a lot...
Ron, you are the MAN! The hoses were swapped. Now it idles around 800 rpm and sounds much much better. I can't figure out why the AC compressor would have caused the rpms to dip under that swapped condition, but it doesn't matter now.

Now I need to see what's going on with my cold idle. I'll start a new thread for that.

Thank you everyone!

~Lenny