Idle Problems, Maybe your IAC is bad.
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,922
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
Idle Problems, Maybe your IAC is bad.
I have been fighting via tuning, an idle problem. Basically I thought due to my camshaft (xe 230/236) it was just causing reversion and my LT1 just wouldnt idle till warm. Also, people reading my logs were saying you have an exhaust leak or a vacuum leak. I chased that forever. So, I wasnt able to run AC in gear at idle, and warm ups were a little tearful due to richness burning my eyes.
According to Data logging, the IAC was working. Wrong, the PCM was working telling the IAC what do do, but it wasnt.
So, I was looking at open loop tune etc for the idle which allot of people do with larger cams.
But I came across this little photo.
http://shbox.com/1/iac2.jpg
Never thought the IAC was bad per sey, because I was expecting a code, which now I know there is none for IAC in the FSM. Just a resistance check. Well I checked mine, AtoB was bad. Bought a new one and WOW it idles on its own immediately, and even allows AC in gear (Kinda lopey, but the IAC is doing what it can to help idle).
So, lessons learned here guys. Just because you dont have a code, doesnt mean you dont have a problem.
According to Data logging, the IAC was working. Wrong, the PCM was working telling the IAC what do do, but it wasnt.
So, I was looking at open loop tune etc for the idle which allot of people do with larger cams.
But I came across this little photo.
http://shbox.com/1/iac2.jpg
Never thought the IAC was bad per sey, because I was expecting a code, which now I know there is none for IAC in the FSM. Just a resistance check. Well I checked mine, AtoB was bad. Bought a new one and WOW it idles on its own immediately, and even allows AC in gear (Kinda lopey, but the IAC is doing what it can to help idle).
So, lessons learned here guys. Just because you dont have a code, doesnt mean you dont have a problem.
Safety Car
Joined: May 2002
Posts: 4,010
Likes: 26
From: Somewhere nowhere
http://forums.corvetteforum.com/show....php?t=1749247
this is my problem....
Mine feels like it has a miss at idle. (when cold)
this is my problem....
Mine feels like it has a miss at idle. (when cold)
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,922
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
http://forums.corvetteforum.com/show....php?t=1749247
this is my problem....
Mine feels like it has a miss at idle. (when cold)
this is my problem....
Mine feels like it has a miss at idle. (when cold)
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,922
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
Basically they should be in the range of 40-80 OHMS.
I cant find a pic of the IAC itself, but the tab you lift off to unplug it is ontop of AB, and CD are the bottom two you check. Remember, you are checking the resistance between A/B and C/D
Melting Slicks
Joined: Oct 2004
Posts: 2,510
Likes: 4
From: Austin Texas
Thanks for sharing Steve! Glad you got your Idle back...
Where do you source your parts in Hawaii ?? Do you have to pay out the wazooo ? Just curious in case I am ever lucky enough to live in Hawaii......
Where do you source your parts in Hawaii ?? Do you have to pay out the wazooo ? Just curious in case I am ever lucky enough to live in Hawaii......
Last edited by MikeC4; Jul 8, 2007 at 04:33 PM.
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Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,922
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
Shipping is deadly. I have had some forum members help me out too.
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,922
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
Dont forget to reset your IAC if you put a new one.
The IAC doesnt get a DTC code, and I bet allot of problems are associated with it wether it is dirty or broke. The datalogging will show it being told what to do. I wish I had known and researched this a long time ago.
The IAC doesnt get a DTC code, and I bet allot of problems are associated with it wether it is dirty or broke. The datalogging will show it being told what to do. I wish I had known and researched this a long time ago.
Now you really have my attention. How I do I reset the summabitch?
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,922
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
Easy.
You open the throttle sligtly, then start the car for about 5 seconds at above idle, since the throtlle is open it will be.
Then shut it off for at least 10 seconds.
Then restart it let idle and you are done, go drive it like you stole it.
You open the throttle sligtly, then start the car for about 5 seconds at above idle, since the throtlle is open it will be.
Then shut it off for at least 10 seconds.
Then restart it let idle and you are done, go drive it like you stole it.
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,922
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
96 LT1
My new scanner arrived today and, guess what, it's telling me that the IAC isn't working either; no reading. On top of that, I'm not getting a MAF reading either.
All the other values are showing up real-time and there is no Check Engine code either stored or lit up.
I'll check the resistance of the IAC wiring to see 'what's up'; I just hope it's the same as your 93 because I can't find my Volume 2 FSM.
Jake
My new scanner arrived today and, guess what, it's telling me that the IAC isn't working either; no reading. On top of that, I'm not getting a MAF reading either.
All the other values are showing up real-time and there is no Check Engine code either stored or lit up.
I'll check the resistance of the IAC wiring to see 'what's up'; I just hope it's the same as your 93 because I can't find my Volume 2 FSM.
Jake
Melting Slicks
Joined: Jan 2005
Posts: 2,604
Likes: 0
From: Phoenix, Arizona
My hotcammed LT4 doesn't like to idle w/ the a/c on (doesn't stall but idle rpms are down & it hunts) until it is in closed loop. Because of this, really can't leave the a/c in the on position when regularly shutting off & restarting the car. Once you are rolling and car goes into closed loop, kick on the a/c and you're fine...kinda funky. 
Sorry for the hijack Steve, this just sort of falls in line w/ what you were initially talking about. Any other cammed LTx's having this issue? Is it common?
FWIW...Due to another idle issue, I recently cleaned the IAC & TB (which worked wonders btw) but that has had zero effect on the a/c situation.
Sorry for the hijack Steve, this just sort of falls in line w/ what you were initially talking about. Any other cammed LTx's having this issue? Is it common?
FWIW...Due to another idle issue, I recently cleaned the IAC & TB (which worked wonders btw) but that has had zero effect on the a/c situation.
Last edited by JEFNLSA; Jul 9, 2007 at 05:29 PM.
Le Mans Master
Joined: Jul 1999
Posts: 8,683
Likes: 6
From: Phoenix AZ
My hotcammed LT4 doesn't like to idle w/ the a/c on (doesn't stall but idle rpms are down & it hunts) until it is in closed loop. Because of this, really can't leave the a/c in the on position when regularly shutting off & restarting the car. Once you are rolling and car goes into closed loop, kick on the a/c and you're fine...kinda funky.
Sorry for the hijack Steve, this just sort of falls in line w/ what you initially were also talking about. Any other cammed LTx's having this issue? Is it common?
Sorry for the hijack Steve, this just sort of falls in line w/ what you initially were also talking about. Any other cammed LTx's having this issue? Is it common?
Anyway, mine will hunt a bit as well with the AC on at idle, but it wasn't quite as bad when I just had heads/cam. How low is your idle going when it's hunting around?
Melting Slicks
Joined: Jan 2005
Posts: 2,604
Likes: 0
From: Phoenix, Arizona
Just be a man and leave the AC off...that's what I do. Oh wait, that's because my AC isn't working right now.
Anyway, mine will hunt a bit as well with the AC on at idle, but it wasn't quite as bad when I just had heads/cam. How low is your idle going when it's hunting around?
Anyway, mine will hunt a bit as well with the AC on at idle, but it wasn't quite as bad when I just had heads/cam. How low is your idle going when it's hunting around?
Hey Jay. 
FWIW, I usually do leave it off but even Bear Grylls (Man vs Wild) would kick on the a/c w/ the temps we've been seeing lately.
Plus, many times I have the wife in the car and she ain't playin' the windows down & no a/c game. To answer your question, my idle is all over the place - between 500 or less & 900 (w/ the a/c on) until she's in closed loop.
Le Mans Master
Joined: Jul 1999
Posts: 8,683
Likes: 6
From: Phoenix AZ
I'd get over to Bills and hook up his scanner, I'd be curious to see what your IAC steps are set at with and without AC. Also, if you haven't been there lately Bills garage has some killer AC going on as well, it's actually nice to go over there and get some work done even in the summer AZ heat!!