Idle issue with A/C on
Thread Starter
Joined: Nov 2001
Posts: 10,060
Likes: 33
From: Canton, GA
Idle issue with A/C on I had the car tuned for WOT and it idles fine with no a/c. When I turn on the a/c it starts hunting a bit, and this causes the a/c clutch to disengage and engage rapidly. So I end up with a surging idle with the a/c on. I am confident this is an IAC issue because if I place a .010 feeler gauge under the throttle stop to crack the blade just slightly it clears up.
The a/c does not cycle if I increases the rpm just slightly. I don't want to adjust the throttle stop because then it will have to idle at 1000 or so. So what are the steps to keep my idle around 750-800 and make it stop hunting?
Forgive me, I used to be a pretty capable tuner 7-8 years ago, but the tuning cells in my brain were ruined by Internet ****
And I do have HP Tuners.
The a/c does not cycle if I increases the rpm just slightly. I don't want to adjust the throttle stop because then it will have to idle at 1000 or so. So what are the steps to keep my idle around 750-800 and make it stop hunting?
Forgive me, I used to be a pretty capable tuner 7-8 years ago, but the tuning cells in my brain were ruined by Internet ****
And I do have HP Tuners.
Teching In
Joined: Jan 2009
Posts: 5
Likes: 0
From: Pine Grove, PA
HPT has tables in the idle section for adders/multipliers when the a/c is turned on. I have run into this a gizilion times. If you can't get it, send me a pm, and ill shoot you my e-mail addy, and you can e mail me the hpt file
There's an "unstable idle" criterion that will shed the A/C
compressor load and cause this, it's to do with the "stall saver"
stuff. But this is the tail, and the head is simply the instability
of the idle (you might find some relief in the A/C bump torque
if it's really the transition, and not A/C-loaded idle instability
in its own right).
I'd bet that the idle is over-enriched, A/C drag raises the MAP
and makes it worse, the mechanical part of the loop gets too
slow and there's your surge.
compressor load and cause this, it's to do with the "stall saver"
stuff. But this is the tail, and the head is simply the instability
of the idle (you might find some relief in the A/C bump torque
if it's really the transition, and not A/C-loaded idle instability
in its own right).
I'd bet that the idle is over-enriched, A/C drag raises the MAP
and makes it worse, the mechanical part of the loop gets too
slow and there's your surge.
Thread Starter
Joined: Nov 2001
Posts: 10,060
Likes: 33
From: Canton, GA
There's an "unstable idle" criterion that will shed the A/C
compressor load and cause this, it's to do with the "stall saver"
stuff. But this is the tail, and the head is simply the instability
of the idle (you might find some relief in the A/C bump torque
if it's really the transition, and not A/C-loaded idle instability
in its own right).
I'd bet that the idle is over-enriched, A/C drag raises the MAP
and makes it worse, the mechanical part of the loop gets too
slow and there's your surge.
compressor load and cause this, it's to do with the "stall saver"
stuff. But this is the tail, and the head is simply the instability
of the idle (you might find some relief in the A/C bump torque
if it's really the transition, and not A/C-loaded idle instability
in its own right).
I'd bet that the idle is over-enriched, A/C drag raises the MAP
and makes it worse, the mechanical part of the loop gets too
slow and there's your surge.
I'd start with disabling stall saver altogether and see if
the A/C cycling goes away. That's, if I recall, just a
checkbox (enable stall saver strategy, or some such).
This will let you cut the problem diagnostically (if the
motor doesn't just flat out die as a result).
Using the bidirectional controls to lock IAC position,
and spark, and selectively let those do their normal
thing, can give you other angles on who's bugging.
Idle VE and spark timing want to be done with the adaptive
spark turned off, so you can see what you're fighting with
no spark-dithering obscuring it. Then you want to turn the
adaptive spark back on, with the tables fixed up - the
underspeed table in a lot of the ones I've seen, is bad
from the factory with a drop to zero at high underspeed
error RPM - fall off a cliff and fail, like.
the A/C cycling goes away. That's, if I recall, just a
checkbox (enable stall saver strategy, or some such).
This will let you cut the problem diagnostically (if the
motor doesn't just flat out die as a result).
Using the bidirectional controls to lock IAC position,
and spark, and selectively let those do their normal
thing, can give you other angles on who's bugging.
Idle VE and spark timing want to be done with the adaptive
spark turned off, so you can see what you're fighting with
no spark-dithering obscuring it. Then you want to turn the
adaptive spark back on, with the tables fixed up - the
underspeed table in a lot of the ones I've seen, is bad
from the factory with a drop to zero at high underspeed
error RPM - fall off a cliff and fail, like.
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Thread Starter
Joined: Nov 2001
Posts: 10,060
Likes: 33
From: Canton, GA
Well I just zeroed out the stall saver and the issue is gone. I still think the IAC counts are a little out of whack, but at least the car will idle without the a/c switching on and off. Thanks Jimmy!
