Idle drops to 500 rpm when AC is ON ???

[Turblown]

Okay... here's the deal... I live in AZ people... need some help here!

I'm trying to pinpoint a problem, so my current setup is Free Mods, K&N Filter and a Tsuedo Muffler. I know Air Conditioning affects performace, but normally idle will only drop 100 or 200 rpm when it is on. Now for some reason my idle is dropping to like 500 rpm and the car almost stalls when I turn on the AC... so I just go without... or turn it off at stoplights.

I was told my ISC (Idle Step Controller) was bad... the last time I took it to the mechanic... but I haven't replaced it yet... could that be part of the problem?? I know the ISC causes Idle surge, etc.... but could it cause this too? Any input would be helpful! Thanks!

 

[steve]

Idle speed dropping when you turn the AC on is a classical indication that your Idle Speed Controller is shot.

Here's how to check it, don't worry that it's a 3S site, the ISC's are the same.
http://www.stealth316.com/2-isc-iac.htm

Steve

 

[00 Agent]

Yep, definately your ISC. Not much else it could be.

 

[unlikely hero]

Is there anything wrong with idling at 500 though? Thats where I have mine set and I love it, so quiet.
=Jason-

 

[00 Agent]

Well you're not going to break anything, but you're going to have dropped voltage from the alternator, incorrect A/F mixture and it will run pretty rough.

 

[sonicnofadz]

I run without an ISC and this is what my car does. I am 100% sure that your isc motor is dead. I removed the AC compressor now so I do don't really have a need for the ISC anymore and my car idles perfectly at 750 rpms (w00t).

 

[Turblown]

Thank you all for reconfirming my suspicions....

I wouldn't mind idling at 500 rpm except for the whole engine starts spazaming like a mother and is NOT quiet.

Well... I will either do one of the many solutions posted on this site...
or just break down and buy an ISC from the dealership... or Ebay.

Thanks again!

 

[unlikely hero]

Funny at 500 rpms she runs smoother than butter. Hmm werid.
=Jason-

 

[Turblown]

Arizona and North Dakota are kinda different climates... but it could just be my car... :thumbdown JK.... I dunno whats up... I just wanna fix it. Thanks for your input though!

 

[98spydert]

It doesn't really mean it's blown... If you're idle screw is adjusted waaay wrong, you're ISC has to make up for it, then when you turn on your AC and the ISC needs to adjust again, it can't. Test it with a ohm meter before you replace it.

 

[Turblown]

Just a long overdue follow up. I replaced the ISC motor and continued to have the same issues. On a whim I just tried swapping out the ECU with a spare I had. A/C worked perfectly. Apparently when I had my capacitors replaced to correct my A/F ratio problems the guy messed up the part of the ECU related to the A/C. I have sold the car since then and I'm focused on my NT rebuild now.

 

[elfroggo]

o cool update 3 years later

 

[Turblown]

o cool update 3 years later

Yeah... ... my bad... ... hopefully the update helps someone.

 

[jredgo1234]

I am having the same problem and can't figure it out. I just got a logger, and have been using it alot. The ISC is around 87 steps when idling, and then when i turn the ac on it moves up to 117 steps. But the idle still goes down to around 500.

Why does the idle decrease as the isc steps are greater to compensate?

Are 87 idleing and 117 with ac on correct step amounts? What are they supposed to be at?

 

[steve]

Apparently when I had my capacitors replaced to correct my A/F ratio problems the guy messed up the part of the ECU related to the A/C.

Possibly, just as likely is that the capacitors leaking had shorted one or more of the ISC driver outputs on the ECU and blown the driver. Or the ISC was bad and when you plugged the repaired ECU in the bad ISC took out the driver again.

In the first case the person replacing didn't know to check a repair the ISC drivers and in the second the mechanic didn't know to check and replace the ISC before installing a "new" ECU.

Thanks for posting back.

Steve