weird idle when i turn AC on

[Crawl]

ok today is the first time ive tried really using the AC since i purchased the car, First thing i noticed was the second i turned it on i went from idleing at around 1k-1200 to <500 , second thing is the AC never got cold, but it probably neesd to be recharged as the car is at 114k miles and who knows when it was done. The idle is the part that threw me off, any thoughts?

 

[steve]

The idle is the part that threw me off, any thoughts?

Bad ISC maybe?

Steve

 

[Staytuned]

Thats normal when the clutch on the AC compressor kicks in and grabs the belt. Your ISC should compensate by increasing the idle a little bit though. Also sounds like you need a recharge.

 

[Crawl]

pardon the newb, ISC?

 

[steve]

pardon the newb, ISC?

Often the best thing to do when you run across something you don't recognize or understand is to do a search on that term. You would be surprised how much you learn that way.

ISC (or IAC in the 2G manuals) = Idle Speed Control. This is the ECU controlled air bypass on the throttle body used for idle RPM management, starting assist, and deceleration control.

The coils that drive the stepper motor inside go bad. If you car idles at 1000-1200 warm it's possible that the ISC is bad since if it was working and the BISS is adjusted correctly, the ECU would use the ISC to lower the idle speed to the factory default of 750 RPM.

Steve

 

[Crawl]

thank you, yeah i shouldve searched that Sorry. so i need a new IAC, whats that gonna cost me haha

 

[steve]

whats that gonna cost me haha

New like $250.

$89 from http://www.crebotech.com/

$50 from http://www.dsmtalk.com/forums/showthread.php?t=129719

They are the same from 91 on. The newest ones (current) look different but interchange.

Steve

 

[oldman]

I would also look into rewiring your fuel pump.

 

[JiveMasterT]

just recharge it and you'll be fine. the idle change is normal... every car ive ever driven does it.

 

[Crawl]

but is it normal for my car to idle at 1200-1500 hot?

 

[steve]

but is it normal for my car to idle at 1200-1500 hot?

No, the car should idle about 750 RPM. When you turn the AC on the idle should quickly settle back down a little higher if the ISC is working. Here's how to check it. http://dmtalon.v8eaters.com/ISC.html

Steve

 

[Crawl]

thanks, im going to find that FAQ on how to adjust the idle screw and do that first then ill test the ISC. Im pretty sure my idle is set high because i have rarely seen my car idle below 1k, if ever .

 

[JiveMasterT]

yeah, it should settle again, but it might take a few seconds. try adjusting the biss.

 

[Crawl]

looked for info on adjusting the BISS, i found teh VFAQ but i had a question, do i really need a scanner to tell me what im idleing at, cant i just asjust it slowly and test what my car is idleing at?