Hotcam guys...
Thread Starter
Le Mans Master
Joined: Oct 2002
Posts: 7,178
Likes: 1
From: Bahston Mass.
Hotcam guys...A/C problem at idle.
Since my engine's been done, when ever I turn on my AC, the idle surges way down, to the point that it SOUNDS like the engine's going to stall.
One person told me to adjust the set screw on the TB to allow more air in, but I would think that would raise the idle??
It was fine before - I added the Hotcam, 1.6RR's, LT4 Heads/Intake(ported) and a few other things. Any suggestions?
One person told me to adjust the set screw on the TB to allow more air in, but I would think that would raise the idle??
It was fine before - I added the Hotcam, 1.6RR's, LT4 Heads/Intake(ported) and a few other things. Any suggestions?
Last edited by JB666; Jul 6, 2005 at 03:08 PM.
Race Director
Joined: Jan 2002
Posts: 12,261
Likes: 85
From: O'Fallon Missouri
Thread Starter
Le Mans Master
Joined: Oct 2002
Posts: 7,178
Likes: 1
From: Bahston Mass.
Thanks!
I subscribed to the thread, I'm curious to see where it goes.
I've talked to Bryan at PCMForless about it, not Alvin. He was the one who suggested the TB adjustment.
I subscribed to the thread, I'm curious to see where it goes.
I've talked to Bryan at PCMForless about it, not Alvin. He was the one who suggested the TB adjustment.
Racer
Joined: Apr 2002
Posts: 342
Likes: 0
From: new orleans La
Originally Posted by JB666
Since my engine's been done, when ever I turn on my AC, the idle surges way down, to the point that it SOUNDS like the engine's going to stall.
One person told me to adjust the set screw on the TB to allow more air in, but I would think that would raise the idle??
It was fine before - I added the Hotcam, 1.6RR's, LT4 Heads/Intake(ported) and a few other things. Any suggestions?
One person told me to adjust the set screw on the TB to allow more air in, but I would think that would raise the idle??
It was fine before - I added the Hotcam, 1.6RR's, LT4 Heads/Intake(ported) and a few other things. Any suggestions?
I have a similar problem with the a/c on my hot cam'd LT4, however mine only stalls or nearly stalls at idle when in open loop. Iac count's with a/c on : 109
Melting Slicks
Joined: Jun 1999
Posts: 2,949
Likes: 23
From: Bowling Green KY
Originally Posted by JB666
Thanks!
I subscribed to the thread, I'm curious to see where it goes.
I've talked to Bryan at PCMForless about it, not Alvin. He was the one who suggested the TB adjustment.
I subscribed to the thread, I'm curious to see where it goes.
I've talked to Bryan at PCMForless about it, not Alvin. He was the one who suggested the TB adjustment.
That just seems like a hack to me - it needs to be done in the tune - if it is idling fine with A/C off but not on it's a software problem not mechanical it seems to me? (granted i ain't no expert either)
Safety Car
Joined: Jun 2004
Posts: 4,197
Likes: 0
From: lafayette co
Originally Posted by JB666
One person told me to adjust the set screw on the TB to allow more air in, but I would think that would raise the idle??
Mine did the same thing after I had the heads ported, and blah blah blah.
Took it in, he adjusted the screw, and it has been fine!
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Drifting
Joined: Jun 2001
Posts: 1,997
Likes: 1
From: Lake Ozark MO
If you don't have the idle set a bit higher then the PCM will try to drive the IAC to compensate for the idle rpm. Unfortunately, the stepper motor is a bit slow and causes the engine to "hunt" quite badly.
The fix is to raise the idle (850-900rpm seems to work quite well) or you can slightly drill out the "straight through" plenum supply hole in the intake itself.
The IAC circuit in the throttle body directs air through ports drilled in the intake that terminate directly to each individual port. The "straight through" or "bypass" port directs air into the plenum itself. With the throttle body off, the flow path is obvious.
Drilling out the direct (to the plenum) port in small stages will allow a nice idle without having to "crack" the throttle blades.
I do recommend cranking up the idle slightly before modifying the IAC flow path. It may provide satisfactory results.
EDIT: If you are running an aftermarket throttle body then they have issues of their own. Typically, their idle ports (from the IAC) do not match well to the intake. Some massaging is needed. My comments apply to a stock style throttle body.
The fix is to raise the idle (850-900rpm seems to work quite well) or you can slightly drill out the "straight through" plenum supply hole in the intake itself.
The IAC circuit in the throttle body directs air through ports drilled in the intake that terminate directly to each individual port. The "straight through" or "bypass" port directs air into the plenum itself. With the throttle body off, the flow path is obvious.
Drilling out the direct (to the plenum) port in small stages will allow a nice idle without having to "crack" the throttle blades.
I do recommend cranking up the idle slightly before modifying the IAC flow path. It may provide satisfactory results.
EDIT: If you are running an aftermarket throttle body then they have issues of their own. Typically, their idle ports (from the IAC) do not match well to the intake. Some massaging is needed. My comments apply to a stock style throttle body.
Last edited by Dan Parker '96; Jul 10, 2005 at 01:03 AM.
Thread Starter
Le Mans Master
Joined: Oct 2002
Posts: 7,178
Likes: 1
From: Bahston Mass.
Originally Posted by Nathan Plemons
I know you said that you subscribed to the other thread but I thought I'd give you a bump and let you know that I've found my solution, I posted it in the other thread. 
Excellent - I just read it - Thanks!
The car actually stalled today with the AC on , it's the first time that happened.
Melting Slicks
Joined: Jan 2005
Posts: 2,604
Likes: 0
From: Phoenix, Arizona
Wow, so I'm not alone w/ this. I have the same problem w/ my hotcammed/BBK'ed LT4. I'm going to get the "Tunercat" software and get this baby running right (never re-tuned since mods) but in the interim is it smart to try & make some adjustments w/ the TB screw (ie idle ajustment)?
Mine doesn't stall but definitely drops down significantly (when I turn on the a/c) in "open loop" but in "closed loop" it seems to find the idle.
I just don't like the way the motor "feels" when I have the a/c on (open or closed loop). A/C off motor runs awesome.
A/C on or off, you can't tell the difference in our BMW but the Vette (on the other hand) seems to really feel the power robbing effects of the a/c.
What's up w/ that?
Mine doesn't stall but definitely drops down significantly (when I turn on the a/c) in "open loop" but in "closed loop" it seems to find the idle.
I just don't like the way the motor "feels" when I have the a/c on (open or closed loop). A/C off motor runs awesome.
A/C on or off, you can't tell the difference in our BMW but the Vette (on the other hand) seems to really feel the power robbing effects of the a/c.
What's up w/ that?
Last edited by JEFNLSA; Jul 12, 2005 at 11:59 AM.
