It could be the throttle position sensor or the idle air control valve.
Idle slows down to a stall when you stop or slow down when AC is running. How do I adjust idle or is something else wrong?
try replacing the idol air control motor.
Check for a vacuum leak either under the hood or under the dash
Timing may be the issue or an idle adjustment
Sounds like your timing is off
sounds like a bad head gasket
on the carb there is a plate that moves when you throttle up and returns to a stop screw when throttled down. This stop screw is the idle adjustment, turn it in until you reach your desired idle rpm.
check and or clean air idle speed motor
More than likely it's your Idle Control Valve.
set the idle down on the carb
bad idle, bad timing, needs tune up , etc.
there is an idle control on these cars, could also be a problem with your intake, and idle. that's what was wrong with my 2000 focus. i lowered the idle, and changed the air filter.