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rough idle when AC is on

14475 Views 20 Replies 12 Participants Last post by  thespud
Any Toyota mechanic on duty here?

I have a 89' corolla with 4AF engine, equipped with carb. The car is idling fine, but when I turn on the AC, the whole steering wheel shakes, it runs real rough.

What do you think it might be?

Thanks in advance
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Not a Mechanic but it seems no one else is posting so Ill throw you a bone. How old is your compressor and is it it good shape? Cuz best I c an think of would be the compressor. Most likely im wrong though however thats the first thing Id look at. Also when you turn on the ac and your under the hood, does anything start making a out of the ordinary sound?
I thought about it, too. I looked under the hood while the AC is on, the compressor is not off balance and no other suspious sound.
My 97 had the same problem. Idle was always pretty rough w/ the A/C on. I always thought maybe it was the motor mounts.

My moms 02 Solara does it as well though, not real bad but still does it, so maybe its just a random toyota thing.
Is the belt too tight maybe? Maybe putting too much torque on the compressor or may bearings in the compressor even?
there is something called "idle up" it is supposed to increase your idle whenever there is a load or the A/C is on

you should look that up in a manual.. go purchase one they cost about 20$

but that might be your problem
I bet that IS the problem. Check the idle up thingy, its on the.. left side of the carb when you look at it from the front of the car.
ya, I have a factory toyota manual for this particular model and year.

I know what you are talking about 2Adanced and Flashman.

When the AC is on, I see the idle shoot up from 750 rpm to 1100.
It's just giving me unacceptable rough idle.

Another thing I haven't mentioned. it happens only when the transmission is drive position. If I put the gear in Park, it idles fine.

Also, I tried; I hold the brake and raise the rpm while it's in drive position with the AC on. It smooths out around 1300rpm. But who wants to set thier idle speed at 1300RPM :)
Ya im having that problem on my 2000 rolla:hammer:
U turn the car on and a/c is switched to the on postion
when u push on the gas the car barely moves it struggles to a crawl. But once U turn off the A/C the car goes.

Am i having the same issues????
The Idle-up valve (IUV) is not just to spike the idle... it also controls it when the a/c is on... if it is broken, it will flicker on and off (or not at all) but will still spike the idle to start with, confusing the compressor, MAP sensor (or AFM) and ECU (if any).

These mixed signals will cause the rough idle that you talk about. When the Throttle Position Sensor (TPS) is open far enough, the IUV switches off as there is no need for the extra Revs to power the compressor. The fact that it idles fine in park is just that there is more load on the engine in Drive, therefore adding to the stresses of the mixed signals from the IUV.

Hope this helps, and if you have any further questions, just ask...
Thepud; you mentioned "idle-up valve", is there another name for the year and model I have?

Like I mentioned on the previous posts. Mine is 89' carubrueted and I have a factory shop manul, but I don't see anything about "idle up"
I'm not too sure what its called on your model, but its there. It will be a small box with vacum hoses that run from the pleunem to the valve, then from the valve to the intake tubing.

All this does is create a loop in the air flow, directly impacting the amount of air flowing behind the semi-closed butterfly(s), thus lifting the idle. The fact that it is carb has no real impact on the a/c as even on EFI controlled cars, the vacum hose bypasses the butterfly(s).

Sorry i cant be of more help as to what it is called, but i specialize in the electronic side of things.
The device is adjustable on the later injected cars, upping the idle helped my rough situation.
Yeah i feel ya, i have an 88 with a 4af and it does the same thing, but it also does it when i turn the steering wheel part of the way to either side.
^^ that is also an issue of increased load on the engine. Assuming of course you have power assisted steering.
so, there is no fix for that?
there is no fix for the increased load... no. as for the rough idle when the a/c is on... there is. Just need to find the real root of the problem, which generally is the IUV.
I got a rougher idle when my AC comes on, but it goes away it I park in it natural
If the rpms on a four cylinder drop too low it will get really rough. The more cylinders you have, the smoother your idle. My 91 idles a bit rough, but when i turn on the a/c, it idles up and there is no roughness. See if your idle is actaully increasing when u turn on the a/c. If its not then do what everyone else was suggesting. If it is, then I don't know what to say. It shouldn't be rough at higher rpms off idle.
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