RPM Drop With AC On

[WhiteCloud]

Every time I turn my AC on, there is an audible "click" and my idle drops from right around 900 to 650 rpm. My Vac reading also drops from 15 in.hg to 10 or 11. It's a PITA to drive the car around with the AC on.

I noticed today that the harness to my ISC sensor was unplugged; I guess I must not have plugged it back in tightly enough after doing the tb shaft seals. So, I plugged it back in, but the problem persists.

I also know I have a boost leak at the BISS screw. I'm going to replace that, and try to readjust my idle. Is it definitely the ISC motor causing the problem?

 

[SoonToBeDSM06]

When you turn the AC on the ISC motor backs out some to keep the engine from stalling. Try disconnecting the battery for like 5-10 mins and connect again after you fix your screw. I had a leak and had to buy the o-ring for it. They sell them at home depot and lowes at like 10 for $1. Ask them for a standard #5 o-ring. Check the coils for your ISC using a multimeter.ISC motor test
If they are bad then looks like you need a new one or go to a junkyard

 

[WhiteCloud]

I just replaced the biss oring--, easiest thing I've ever done to my car!

Problem has not been solved yet. I am going to reset the ecu like you suggested, then hook it back up with the ISC harness plugged in. The thing is, I never popped an CELs, even with the ISC motor unplugged.

If the problem persists, I will check the ISC. I don't own a multimeter, though, and would rather not go buy one.

Thanks for the help--I'll report back in a bit.

 

[WhiteCloud]

Reset the ecu, plugged in the ISC harness, and no change.

I'll be testing the ISC tonight with a buddy's multimeter to see if it is blown.

 

[T2Small]

Normally, the RPMs should increase when you turn the A/C on. The ECU instructs the ISC to open up a little more increasing RPMs.

There are several reasons why this could be happening. It would recommend treating it similar to an "idle surge" issue as the ISC isn't doing what you want.

Try testing your ISC:
http://dmtalon.v8eaters.com/ISC.html

And check your TPS adjustment:
http://www.plymouthlaser.com/tps.htm

There are lots of other good links at:
http://www.vfaq.com/FAQlocator-intake.html (Throttlebody section)

Good luck!

-Kevin

 

[beatshack]

my car does this too.. rpm drop by about 200 rpm and i lose what feels like 30whp, which i know is normal but if feels like a huge loss.

just a note for people not wanting to pay $200 for a TPS from the dealership - lots of hyundai's share the same MAS, TPS, throttle body, intake, etc.. I replaced my TPS with a hyundai tps in a junk yard (looked the same so i thought why not try it) and it solved my erratic bucking in low rpm.

 

[WhiteCloud]

Just replaced the ISC with a used unit I bought for $35 on DSMtrader. Even though the used ISC looked like shit compared to mine after I pulled it, I cleaned the old one off and it worked like a charm.

The VFAQ about the ISC testing/replacement under Intake is terrific. The swap out process took about a half-hour, including removing the battery tie-down and cleaning the old ISC before installation.

My idle now rises higher upon initial startup, then settles to 800 rpm. When I turn the AC on, it kicks up to about 900 rpm. I suspect the loss of power with the AC on is typical of 4 cylinder engines, regardless of how the ISC is working.

If you suspect your ISC is the culprit of your AC/idle problems, test it and replace it!

 

[poppyseed]

My idle is low to when the A/C is on but i would find it hard to believe that the IAC is bad because the car idles perfect, and when the A/C is on and the compressor kicks on you can see the vacuum move which then goes back to its original state before the compressor kicks off telling me that the IAC is moving to allow more air around the throttle body, plus i can idle up a hill and still be perfectly smooth.

 

[philly5eagle]

I have another post on here about the idle drop on mine when I turn the a/c on. Did the isc test bad on yours before you replaced it? I cked the ohms on mine and they are correct and the car idles fine w/out the a/c on. Could the isc still test ok when i ck the ohms but still be bad?