93 civic erratic idle with a/c
 

Hello. I just got my a/c system checked for leaks and recharged for the first time since I own this car. Before that the idle has been smooth for the most time. I have rebuilt the engine. The cold idle valve has been cleaned and checked, works perfectly, when cold engine rpms at about 1200 when warm it closes all the way and rpm go down to 800 (where I programmed it).

Now with my new a/c system the rpms are fine when cold, but when warm it will be erratic. Sometimes it will be at 800 and feel fine, sometimes it will go down to 200 and back up several times at a trafic light. Sometimes it will go way down to almost stall then come back up to 1000 and run normal with no change.

It seems when I let go of the gas pedal and press the clutch (neutral) the rpms go down fast and stay down sometimes.

The IACV has been cleaned before, and without a/c the car idles fine. Is there a way I can test the IACV. Or should I be checking something else?

Thanks in advance.

Make sure that the condenser fan works. It should be running all the time the compressor is engaged.

The idle speed is not adjustable unless you have a chipped ECU. It's going to idle where the ECU wants it to, as long as the IACV can keep up. In particular, don't adjust the little screw that physically stops the throttle plate lever. This is not used to set the idle speed.

You may get some benefit from opening the air screw on the top of the throttle body. Warm up the engine and turn off the A/C and every other electric option. Unplug the wires to the IACV(*). The idle should slow down to about 450. If the engine wants to stall, turn the air screw counterclockwise to let in more air.

(*) This will turn on CEL with a code 14, which of course should be ignored because you caused it by unplugging the plug. Clear the ECU after doing the adjustment so you don't have an old code causing confusion.

Sorry, that is what I meant by programming the idle. I never adjust the throttle plate, that is flat (.45v at tps). I had adjusted the screw to an adle of about 500rpms i think. The car idles normallly at 800rpm. I know the fan does turn on with the a/c, but I will connect a multimeter to it to make sure it stays on at all times when driving.