Rough Idle When Compressor is On?

[justakid]

I have a '94 ATX SHO with just south of 200k miles on it. I had its first (!) 60k done at about 180k miles which alleviated most of my engine troubles, sans my rough idle (on occasion).

Anyway so yesterday it was idling really rough (like the dash board was moving up and down a quarter of an inch) and I decided to see if shutting my A/C off made any difference, it did.

I've since noticed that anytime it idles rough turning off the compressor (ie I can put the A/C on vent and it stops as well) fixes the idle, the promblem also does not occur when the car is in park.
Anyway I know very little about cars, I've tried resetting my idle per SDPatt's instructions and that seemed to help some but the problem persists and so I consult the SHO gurus ;-)

Any help or advice would be appreciated, let me know if you guys need any more details.

Thanks,
Wes

<small>[ July 28, 2003, 04:13 PM: Message edited by: justakid ]</small>

 

[rangerj]

justakid,

Without knowing the A/C system pressures I am guessing. Here are some possibilities.

A/C compressor is about to sieze
A/C pulley bearing about to sieze
System pressures very high do to; blockage of condenser, oriface, accumulater, or evaporator,
moisture in the system, lack of oil in the system
idler pulley about to sieze

Check your system for signs of leaks. Check the evaporator for signs of icing up. Are your A/C lines cold or hot?

The idle problem you describe indicates a definite drag on the engine when the A/C is on, but without additional information I cannot tell you why. rangerj

 

[justakid]

The Compressor is "new" as of December, I'm not sure what all was replaced with it but I followed what I read here (evaporator, some other stuff). I checked the pressures and they were a little high (4-5lbs) so I released some of the coolant and I guess we'll see if that helped.

I'm not sure about the idler/ A/C pullies, is there a way to check those (easily)? As far as checking for leaks, I put coolant in the system about 3 weeks (including 2oz of "oil" and some leak stopper stuff) ago and it seems to be about the same pressure (within 2-3lbs) I'm not sure what "A/C lines" are (I'm a total car noob ;-) but the metal pipe near the low pressure valve (where I added coolant) has ice on it. Again, thanks for the help and if I can provide any more information that would be helpful, just let me know.

Thanks again,
Wes

 

[projectSHO89]

I would focus on the IAB valve.

When the PCM commands the AC clutch to energize, it precedes this with an idle adjustment in anticipation of the load to come.

If the IAB valve is malfuctioning, it can act like a big vacuum leak...

BTW, AC system pressures can vary by 10's of pounds based on a number of variables including the ambient temperature and other operating parameters.

Steve


Steve

 

[justakid]

Is there any way to test the IAB?

Thanks,
Wes

 

[SHO_Driver]

Instead of testing it just go ahead and clean it. With that much mileage it should be done regardless. Do a search for the exact procedure or check out shotimes.com.

 

[svtman]

Sounds to me like the lower idle is causing the problem. Try it again and give the car a little gas and see if the higher idle fixes it. It may be the IAB like mentioned above, or your idle may need a slight adjustment to fix.

 

[projectSHO89]

Idle speed is "not adjustable". See the emissions control decal.

Steve

 

[svtman]

Right - what I meant is that other factors may be contributing the the low idle - Vacuum leaks, PCV system failures, EGR valve leaks and carbonned-up throttle bodies all affect idle quality and control. Make sure these are clean first and run your codes to verify they are not throwing any. Then, try resetting your computer so the car can relearn its idle.

 

[justakid]

I cleaned my throttle body/intake/EGR valve/IAB (per the intructions here, with Berryman's B-12 Chemtool) about 2 months ago and that greatly improved my idle (as did resetting the idle) but on occasion I still have a rough idle (it used to ALWAYS idle rough) the only code I'm throwing right now is the car is running lean (I need new O2 sensors, me thinks, but I've yet to successfully run the KOER test)

Anyway, would there be any other signs that the IAB is bad? I'm sure it could use replacing after 200k miles I just hesitate to spend $70 (FPN) and still have an idle problem (Call it poor college student syndrome ;-) I do appreciate all the help you guys have offered; you have no idea how much you've all helped me to be able to drive an SHO, despite my noobness ;-)

Thanks,
Wes