I have a 2000 Escort ZX2 stick shift with about 40k miles on it. WHenever I have the AC/heat turned on the car stalls when I put in neutral or downshift to first to come to a stop... Occasionally it won't stall but the RPMs will drop to about 250 and the car will try to stall for a minute but then kick back up to 1000 RPMs... It only happens if I have the AC turned on or if I have heat going. Can run cool air fan without AC but not warm air. Had a full tune up, had the fuel filter and pump checked and cleaned...Any ideas?

Thank you.

IAC? Idle Air Control...right on top of your throttle body...my guess.....my car does the same thing, but that's part of a WHOLE different issue

check teh air sensor

That's odd... not sure why it would only happen when the AC is running. It NEVER happens when you don't have the accessories running?
I would suspect vacuum leak, but the AC thing is a twist. In addition to the things mentioned above, check your alternator output when those things are running. I wonder if the high idle is working...