Hi guys. I recently purchased a 2nd-hand honda civic 2000 (D16Y7) M/T. Now i'm having problems w/ the idle speed when the Air conditioning's on; when at idle- it's a little bit low & sometimes will almost turn the engine off, and when accelerating- the car losses power and lags before actually moving (this happens at 1st & 2nd gears). With A/c on, when I step on the gas pedal the engine doesn't rev, I should do it several times atleast before it'll rev...

I tried two mechanic shops already but to no avail. First, they cleaned the Throttle body/IACV & replaced the IACV. And then, they again cleaned the IACV, flushed engine coolant, & replaced the Spark plugs. BTW, there are no "check engine" lamps on. I also tried to reset the ECU by unplugging the backup fuse, but still the same problem. I'm totally lost now & hoping for all your expert's advise.

 

Make sure that the condenser fan works. The fan should be on all the time the compressor is engaged. If it doesn't work the condenser will overheat which causes pressure to increase and the compressor to pull excessive horsepower.

There is another problem with the driveability, as the A/C won't make the engine "lag" that much. The car will be noticeably slower but it should always rev immediately when you press the gas in neutral.

 

Yes, the condenser fan works all the time the compressor is engaged. Though I've noticed that with a/c on, the compressor spins erratically. When it spins normally, steppin on the gas pedal has no issues. But when the spinning's unstable, here the problem comes in (as I mentioned about when stepping on the gas pedal and the engine doesn't rev instantly). Could this be a particular compressor problem? As I want this fixed very badly. Weather here is "extremely hot" especially in summer.

 

If the idle gets too low, the ECU will drop out the compressor temporarily, it will click on and off trying to prevent stalling.

Assuming the car's wiring is stock, this really sounds like an engine problem not so much an A/C problem. When you are driving on the road, you get steady cool air, right? There's an outside chance it's badly overcharged but then it wouldn't cool well on the road either. Pressures should be checked but that requires the engine to run well enough to run it steady at 1500 rpm or so.

Your mechanic has done the usual correct things regarding unsteady idle, but it must be something else. Run the fundamental checks like spark timing and check for dead cylinders. Check the charging system. Be sure the passages leading to the IACV are clean. Set up the base idle speed with the air screw. I'd also check the TPS with a voltmeter, a bad TPS should throw a CEL code, but don't count on it.

By the way, your check engine light is functional, right? It should come on to test the bulb every time you turn the key on but don't start. If it NEVER comes on at all, someone has removed the bulb or otherwise disabled it. That's very common on used cars.

 

Thanks for your always quick responses, I really appreciate. About the CEL indicator, yes it's working just fine. Well actually me & my friend tried some adjustment on the "Throttle stop screw" inorder to increase the idling a little. As to our surprise, the idling worked fine with A/C ON. Also, the ECU is not shutting down ON & OFF the compressor as you mentioned earlier. While running though, there's a little noticeable loss of power when shifting to 2nd gear, but once it picked up, everything's good.

Only the problem now is that the idling goes up & down when the A/C off...Any thoughts..?

 

Problem came back just today... With A/C on, idling drops....

 

Take the IACV off and make sure the passages in the manifold leading to it are clear.

The throttle stop screw should not be adjusted. There is another air screw on the TB that lets air around the throttle plate. It is a big screw turned with a flat screwdriver. Open it (turn counterclockwise) as far as possible yet still have a normal idle with the A/C off.

 

Have you replaced the plug wires and inspected the inside of the distributor cap and the rotor? Look for corrosion, wear, or damage at the contact points or anywhere inside the distributor.




Also hook up a timing light and check the ignition timing:




Here's how to properly adjust the idle speed:

 

I had my A/C system cleaned. My new mechanic found some pressure problem due to clogging, he said this could cause the idling to drop because of the compressor using more power. They replaced the condenser and the expansion valve, cleaned everything...Well it improved a lot in terms of cooling but still didn't solve my issue w/ the idling. The pressure problem is gone by the way. Now they want to check on the distributor... in your reply you mentioned about checking the distributor, I'm just hoping that this could put an end to my agony. My spark plugs was just replaced in a week, but we found some carbon fouling over all (4) plugs.

 

Have you tried the idle adjusting screw yet? Also reset the throttle stop screw to stock. It should stop the throttle plate just as it closes fully. At idle you want the throttle plate to be fully closed but the screw is there so it doesn't slam against the sides of the throttle body.