A/C idle?
A/C idle? A little background: I have a 221/221 .558 114 cam in a 99 TA with an A4 and a 3200 stall. When I first installed my cam, instead of running rich like most everyone else, I was way lean. Sent my PCM in for a mail order tune. Runs great now except for when I turn the A/C on. When it is on, the idle increases a few hundred RPM, and the car will accelerate by itself to about 45 MPH. I have called the shop that tuned it, and they say I have a vacuum leak. Well, I have checked every vacuum line I know of, and the all appear to be on good.
Near the end of this summer, sometimes it would idle OK with the AC on, but about 90% of the time, it would still accelerate with my foot off the gas.
My question:
Is there a specific idle table for when the A/C is on? And could they have programmed it too high?
Is my normal idle too high, so that when the A/C is on that idle becomes way too high causing the acceleration?
Do I need to drill a hole in my TB?
Do I have a vacuum leak I can't find?
TIA
Near the end of this summer, sometimes it would idle OK with the AC on, but about 90% of the time, it would still accelerate with my foot off the gas.
My question:
Is there a specific idle table for when the A/C is on? And could they have programmed it too high?
Is my normal idle too high, so that when the A/C is on that idle becomes way too high causing the acceleration?
Do I need to drill a hole in my TB?
Do I have a vacuum leak I can't find?
TIA
It sounds like a tuning issue to me. Actually, it sounds like you are getting a cruise control effect with the a/c on. I had a buddy that had this problem and we tuned it out. If I remember correctly we adjusted his Running Airflow table in edit.
Originally Posted by HC02SS
It sounds like a tuning issue to me. Actually, it sounds like you are getting a cruise control effect with the a/c on. I had a buddy that had this problem and we tuned it out. If I remember correctly we adjusted his Running Airflow table in edit.
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TECH Senior Member
Joined: Nov 2001
Posts: 7,036
Likes: 1
From: Lake Zurich, IL
Well I'm notta tuner 
but there is a seperate table for idle RPM w/AC on ... there's settings for in gear and in park...
However the acceleration to 45mph definetly sounds like unmetered air is entering the car... are you sure it only occurs w/the AC on?
w/a larger stall converter the idle speed in gear shouldn't be enought to move the car much... 45mph is at least 2nd gear floored, gradual would be overdrive ... and it'd take alot more than a few hundred RPM to cause a convertered car to gradually climb to such speeds ...
However if it only occurs w/the AC on then it is definetly a tuning issue... the AC system isn't designed such that there is ANY possibility of cool air being sent to the engine heh ... though theoretically... since AC puts the car under higher loads... increased crank case pressure ... so maybe air via the PCV? (if that was the case though you'd have tons of missing power and woudl be burning alot of oil)
Do you have access to a scan tool of any kind? I'd be interested on what your IAC is doing during the acceleration... Also you can check yourself for any leaks... use any flammable (this is key... must be flammable) spray ... and spray around your intake to maf ... then spray around the intake manifold ... if the engine reacts to this (increasing RPMs) then you have unmetered air entering the car (air is being sucked in past the MAF)
if you don't have this (unmetered air) then it has to be tuning...
Where are you located? perhaps there's someone nearby on the boards that can either scan your car or read your PCM to see what's going on.....
but there is a seperate table for idle RPM w/AC on ... there's settings for in gear and in park... However the acceleration to 45mph definetly sounds like unmetered air is entering the car... are you sure it only occurs w/the AC on?
w/a larger stall converter the idle speed in gear shouldn't be enought to move the car much... 45mph is at least 2nd gear floored, gradual would be overdrive ... and it'd take alot more than a few hundred RPM to cause a convertered car to gradually climb to such speeds ...
However if it only occurs w/the AC on then it is definetly a tuning issue... the AC system isn't designed such that there is ANY possibility of cool air being sent to the engine heh ... though theoretically... since AC puts the car under higher loads... increased crank case pressure ... so maybe air via the PCV? (if that was the case though you'd have tons of missing power and woudl be burning alot of oil)
Do you have access to a scan tool of any kind? I'd be interested on what your IAC is doing during the acceleration... Also you can check yourself for any leaks... use any flammable (this is key... must be flammable) spray ... and spray around your intake to maf ... then spray around the intake manifold ... if the engine reacts to this (increasing RPMs) then you have unmetered air entering the car (air is being sucked in past the MAF)
if you don't have this (unmetered air) then it has to be tuning...
Where are you located? perhaps there's someone nearby on the boards that can either scan your car or read your PCM to see what's going on.....
Originally Posted by horist
Well I'm notta tuner but there is a seperate table for idle RPM w/AC on ... there's settings for in gear and in park...
However the acceleration to 45mph definetly sounds like unmetered air is entering the car... are you sure it only occurs w/the AC on?
w/a larger stall converter the idle speed in gear shouldn't be enought to move the car much... 45mph is at least 2nd gear floored, gradual would be overdrive ... and it'd take alot more than a few hundred RPM to cause a convertered car to gradually climb to such speeds ...
However if it only occurs w/the AC on then it is definetly a tuning issue... the AC system isn't designed such that there is ANY possibility of cool air being sent to the engine heh ... though theoretically... since AC puts the car under higher loads... increased crank case pressure ... so maybe air via the PCV? (if that was the case though you'd have tons of missing power and woudl be burning alot of oil)
Do you have access to a scan tool of any kind? I'd be interested on what your IAC is doing during the acceleration... Also you can check yourself for any leaks... use any flammable (this is key... must be flammable) spray ... and spray around your intake to maf ... then spray around the intake manifold ... if the engine reacts to this (increasing RPMs) then you have unmetered air entering the car (air is being sucked in past the MAF)
if you don't have this (unmetered air) then it has to be tuning...
Where are you located? perhaps there's someone nearby on the boards that can either scan your car or read your PCM to see what's going on.....
but there is a seperate table for idle RPM w/AC on ... there's settings for in gear and in park... However the acceleration to 45mph definetly sounds like unmetered air is entering the car... are you sure it only occurs w/the AC on?
w/a larger stall converter the idle speed in gear shouldn't be enought to move the car much... 45mph is at least 2nd gear floored, gradual would be overdrive ... and it'd take alot more than a few hundred RPM to cause a convertered car to gradually climb to such speeds ...
However if it only occurs w/the AC on then it is definetly a tuning issue... the AC system isn't designed such that there is ANY possibility of cool air being sent to the engine heh ... though theoretically... since AC puts the car under higher loads... increased crank case pressure ... so maybe air via the PCV? (if that was the case though you'd have tons of missing power and woudl be burning alot of oil)
Do you have access to a scan tool of any kind? I'd be interested on what your IAC is doing during the acceleration... Also you can check yourself for any leaks... use any flammable (this is key... must be flammable) spray ... and spray around your intake to maf ... then spray around the intake manifold ... if the engine reacts to this (increasing RPMs) then you have unmetered air entering the car (air is being sucked in past the MAF)
if you don't have this (unmetered air) then it has to be tuning...
Where are you located? perhaps there's someone nearby on the boards that can either scan your car or read your PCM to see what's going on.....
I am in the process of purchasing Autotap. I had borrowed it before, but didn't know what to look for. What should my IAC be doing during acceleration?
What kind of flammable spray would you recommend? (preferably something that won't make a mess or discolor stuff) How much would the RPMs raise? would I be able to tell a difference?
I am located in Utah (near Salt Lake City) - if anyone lives around there and could help me out, I would appreciate it.
Thanks for you help too, horist.
TECH Senior Member
Joined: Nov 2001
Posts: 7,036
Likes: 1
From: Lake Zurich, IL
I've used brake cleaner in the past (make sure it doesn't say non-flammable), it will prolly raise several hundred RPMs... if your car idles smooth now it'll be a very noticable audible change
if you're getting alot of unmetered air going in, the Idle Air Count will be 0... the PCM will be commanding that the TB blade be closed as much as it can control, but air is still sneaking in from somewhere feeding combustion ... this is w/your foot off the gas of course
Just the fact that it only happens when the A/C is on seems odd... but doesn't hurt to check for a leak somewhere (just spray a lil amount of the flammable spray around the intake manifold and Throttle Body and listen for the change... don't spray anything through the air box or through the MAF
if you're getting alot of unmetered air going in, the Idle Air Count will be 0... the PCM will be commanding that the TB blade be closed as much as it can control, but air is still sneaking in from somewhere feeding combustion ... this is w/your foot off the gas of course
Just the fact that it only happens when the A/C is on seems odd... but doesn't hurt to check for a leak somewhere (just spray a lil amount of the flammable spray around the intake manifold and Throttle Body and listen for the change... don't spray anything through the air box or through the MAF
