IAC or vacuum leak?
Thread Starter
Registered User
Joined: Jul 2005
Posts: 297
From: Wisconsin
IAC or vacuum leak?
Still working on ironing out a couple minor bugs after my LE2 build. Currently my IAC counts are maxed out at 160. They drop to around 100 at around 2000 RPM. I am running a 58mm summit throttle body, how to I figure out if this is a problem with my throttle body or a bad vacuum leak?
Registered User
Joined: Dec 1969
Posts: 27,725
From: Little Rock, AR
If you had a vacuum leak, the counts would be closer to 0 than 160. Perhaps you need to adjust the throttle stop to let in more air (you would have to adjust/correct the TPS after doing this). That should let more air in and allow the IAC counts to drop.
Registered User
Joined: Dec 2003
Posts: 710
From: Fort smith, AR
just out of curiosity.. would an old battery cause voltage problems like im getting those codes for?
Registered User
Joined: Jun 2006
Posts: 2,092
From: lakeville, pa
by correcting the tps do you mean opening the screw holes up a little and moving it to read zero at the stop
Registered User
Joined: Dec 2003
Posts: 710
From: Fort smith, AR
Registered User
Joined: Jul 2006
Posts: 239
From: Tempe/Phoenix
so how do you adjust the tps after adjusting the idle screw (iac)?
i guess im no the only one who has to do this still
also, sometimes my car starts up at LOW rpms (barely going, but quickly rises to normal idle speed), could this be the IAC as well?
i guess im no the only one who has to do this still
also, sometimes my car starts up at LOW rpms (barely going, but quickly rises to normal idle speed), could this be the IAC as well?
Registered User
Joined: Nov 2006
Posts: 869
From: Houston(clear lake)
I believe they slot the holes for the TPS to make it adjustable. Not exactly sure have not had to do it yet. I will be down that road soon im sure.
Administrator
Joined: Nov 1998
Posts: 71,094
From: Hell was full so they sent me to NJ
The PCM expects to see the TPS closed throttle voltage between 0.20 and 0.90V. As long as it is within that range, it baselines that voltage as 0% throttle position, and prorates the TPP% by adding about 4.0V to get the WOT voltage.
To adjust a new throttle body, hook up a scanner. If the idle is above spec, back off on the throttle stop screw slowly until the idle hits spec. Look at the IAC counts and fine-tune the stop screw until the IAC counts are between 20-40 on a stock engine. They should probably be a bit higher on an engine with a beefy cam. Once you have the idle and the IAC counts correct, you look at the TPS voltage, and make sure it is between the values noted above (0.20-0.90V). If it isn't, you have to slot the screw holes and rotate the TPS sensor until it is.
Some people feel that getting the TPS closed throttle volts in the range of 0.50-0.67V is preferred, so if that's important to you, that is another reason you might want to slot the screw holes.
To adjust a new throttle body, hook up a scanner. If the idle is above spec, back off on the throttle stop screw slowly until the idle hits spec. Look at the IAC counts and fine-tune the stop screw until the IAC counts are between 20-40 on a stock engine. They should probably be a bit higher on an engine with a beefy cam. Once you have the idle and the IAC counts correct, you look at the TPS voltage, and make sure it is between the values noted above (0.20-0.90V). If it isn't, you have to slot the screw holes and rotate the TPS sensor until it is.
Some people feel that getting the TPS closed throttle volts in the range of 0.50-0.67V is preferred, so if that's important to you, that is another reason you might want to slot the screw holes.
Registered User
Joined: Dec 2003
Posts: 710
From: Fort smith, AR
yes, that is how its done.. Then you will need some way to monitor the voltage in idle position and wide open throttle position. There is a tutorial on the site for this somewhere..
Registered User
Joined: Dec 2003
Posts: 710
From: Fort smith, AR
The PCM expects to see the TPS closed throttle voltage between 0.20 and 0.90V. As long as it is within that range, it baselines that voltage as 0% throttle position, and prorates the TPP% by adding about 4.0V to get the WOT voltage.
To adjust a new throttle body, hook up a scanner. If the idle is above spec, back off on the throttle stop screw slowly until the idle hits spec. Look at the IAC counts and fine-tune the stop screw until the IAC counts are between 20-40 on a stock engine. They should probably be a bit higher on an engine with a beefy cam. Once you have the idle and the IAC counts correct, you look at the TPS voltage, and make sure it is between the values noted above (0.20-0.90V). If it isn't, you have to slot the screw holes and rotate the TPS sensor until it is.
Some people feel that getting the TPS closed throttle volts in the range of 0.50-0.67V is preferred, so if that's important to you, that is another reason you might want to slot the screw holes.
To adjust a new throttle body, hook up a scanner. If the idle is above spec, back off on the throttle stop screw slowly until the idle hits spec. Look at the IAC counts and fine-tune the stop screw until the IAC counts are between 20-40 on a stock engine. They should probably be a bit higher on an engine with a beefy cam. Once you have the idle and the IAC counts correct, you look at the TPS voltage, and make sure it is between the values noted above (0.20-0.90V). If it isn't, you have to slot the screw holes and rotate the TPS sensor until it is.
Some people feel that getting the TPS closed throttle volts in the range of 0.50-0.67V is preferred, so if that's important to you, that is another reason you might want to slot the screw holes.
Registered User
Joined: Jun 2006
Posts: 2,092
From: lakeville, pa
thanks alot fred much appreciated, somehow i overlooked this, and i am having some low idle issues when cold too, gonna try this tomorrow
is there any specific reason i would want the voltage to be between .5 and .6 rather than .2 and .9
is there any specific reason i would want the voltage to be between .5 and .6 rather than .2 and .9
Last edited by dangalla; Oct 24, 2007 at 09:05 PM.
Administrator
Joined: Nov 1998
Posts: 71,094
From: Hell was full so they sent me to NJ
I can't recommend a specific number. It may take a bit of trial and error, depending on the specifics of the cam. It just makes sense to give the IAC motor more "headroom" with a larger cam and its inherent unstable idle. There are also ways to stabilize the idle using the timing tables.
Registered User
Joined: Dec 2003
Posts: 710
From: Fort smith, AR
I can't recommend a specific number. It may take a bit of trial and error, depending on the specifics of the cam. It just makes sense to give the IAC motor more "headroom" with a larger cam and its inherent unstable idle. There are also ways to stabilize the idle using the timing tables.
Registered User
Joined: Dec 2003
Posts: 710
From: Fort smith, AR
I also answered a question for you. My question was pertaining to the IAC which was relevant to the thread too.. Maybe we should both start our own thread?