95 honda civic ex idles up and down but when ac is on it stops?

Question

My 95 honda civic ex idles up and down, but when i turn the ac on it stops. Is it the vacuum hose or a sensor?

Answer 1

there is an idle air control valve that regulates the engine idle speed.  that valve is essentially an electrically operated plunger that extends into an air passage to meter the amount of air that bypasses the throttle plates to give you a stable idle.  if its jumping up and down one of two things is happening--either the valve isn't working (most likely) or the air passage is clogged with carbon (think of soot in a chimney).

when the AC is on you have a separate idle speed control program that the PCM executes to factor in the additional load placed on the engine by the AC.  the Idle air control valve retracts to allow near the maximum amount of air through the passage when the AC is ON.  

my guess is that the Idle air control valve is sticking from carbon build up.

typically you have to replace the valve and clean the passage to eliminate the problem.  the valve is located under the throttle body and has two vacuum lines and one electrical connector going to it

hope that helps