Idle with A/C on...

[xtremeskier97]

Ok...I have searched and could not come up with anything like what Im dealing with.

My car idles good with no A/C on, at about 850, which I think is the standard idle on our cars but not for sure. But when I turn on the A/C, the idle drops and the steering wheel starts shaking like mad. If I rev it just a bit, say to about 900-950, it's fine.

I was under the impression that when the A/C is kicked on, the idle was supposed to adjust up to compensate for the drop. Is this not the case? If this IS true, how can I go about correcting my problem?

Thank you for any help/direction.

[moneypitaccord]

not too sure bout the idle on the automatics but you can try to adjust the screw on the throttle body up just a little to compensate and also on the thing thats right to the left of the iac valve there is a allen wrench adjustment that changes the idle also hope this helps

[evol90accord]

Yes, your idle is supposed to go higher to compensate but mine does it too. I don't know what causes that. You can feel the compressor engage at a stoplight and the idle drops to about 600 or 700 and usually it bounces back up, but not always.

I'd hate to adjust the idle screw just for that, because my idle is already about 200 rpm higher than stock.

I'd also like to know what to do about this, if you can do anything that is.

[mrhonda]

not too sure bout the idle on the automatics but you can try to adjust the screw on the throttle body up just a little to compensate and also on the thing thats right to the left of the iac valve there is a allen wrench adjustment that changes the idle also hope this helps

NO....don't do that, the idle screw is to adjust base idle which should be around 750. Does the idle compensate at all and just seems slow and lazy, or does it just drop really low and stay there? If it just seems lazy, try cleaning out the IAC valve and run some top engine cleaner thru the engine. A rough idle in general can be caused by alot of things....broken motor mounts, out-of-time balance shafts, or the engine just needs a good tune-up.

[xtremeskier97]

No...it doesnt seem to compensate at all. It just drops lower. I just replaced the from mount with energy suspension supports, so that one isnt the problem. Ill try a general tuneup and see what happens.

Ill report back.

[evol90accord]

I just replaced the from mount with energy suspension supports, so that one isnt the problem.

yeah, but what about the other 3? I know my side mounts are completely split, and I'm actually afraid to look at the front and rear mounts *shivers*

[xaxis360]

Okay. Three things

1. If the engine isn't compensating at all, the ECU might not be receiving the A/C on signal. It's supposed to adjust the timing and immediately raise idle (if necessary) to make the compressor engagement smoother. As soon as you press the button when the engine's warm, it should spike the idle a few noticible RPM's just a bit before the compressor engages.


2. You replaced the front torque rod. Why? Was the original one bad? If so, how long? If it was a long time, you probably ruined your rear mount. My front torque rod was bad when I bought my car... who knows how long. I replaced it, but shortly thereafter, the rear went and I got vibration and a loud THUD! when I put the car in reverse when it was cold.

The first thing to check on an auto is the vacuum-activated system on the rear mount.
You can find a good article here on idle vibration.

3. I wouldn't try adjusting the idle screw. There is obviously something wrong elsewhere if the car idled okay before this problem. You'll just be covering up another problem if you do that.

[xtremeskier97]

OK..just to clear one thing up. My car is a manual, not auto.

I say "replaced", but it actually isnt replacing the front mount, it's reinforcing it with the energysuspension mounts. I did that just about a week ago. Before I got the a/c charged.

The car doesnt try to compensate at all. The idle just goes down and the steering wheel starts shaking like mad. With the engine cold or hot, it does the same thing.

[evol90accord]

Good article though... thanks.

[xaxis360]

Its prolly the A/C signal going to the ECU. The ECU has no clue that the compressor is about to engage, and in turn, you experience low idle and vibration cause the computer has no clue what's going on. There is a freak chance that its the alternator FR signal going to the ECU. That signal instructs the ECU to compensate for the load of the alternator when it is charging.

Honestly auto or manual, if the front mount is okay, the most common culprit is the rear when you get a lot of vibration.