Iac?
Thread Starter
2nd Gear Member
Joined: Mar 2008
Posts: 232
From: South Carolina
man, i was out today and herd a stang go by and it sounded sooo good. i just wish i could get mine running right. i got so much crap for it havnt installed because i want to get it running right first. i got a valve tap wich is really loud on a cold start but quietens down after about 10 minutes. i have a loss of power, she feels like she wants to go but kinda feels like she is sufacating (<---spell check). Im just trying to figure out if it is simple crap first because im broke as hell, the mechanic who did the pi swap charged me 1600 bucks wich was originally supposed to cost 600.
If the timing is off 1 tooth, i dont think i would have been able to drive it for the 2000 miles ive put on it so far. everyone i talk to says that if its off 1 tooth, it would destroy my valves and pistons.
If the timing is off 1 tooth, i dont think i would have been able to drive it for the 2000 miles ive put on it so far. everyone i talk to says that if its off 1 tooth, it would destroy my valves and pistons.
TECH SAVANT
Joined: Dec 2006
Posts: 10,937
From: Saint Augustine, FL
I know exactly how an IAC works. I guess I should have rephrased what I ment. It does help "stabilize" the idle but again it does not control it. You can delete the IAC all togather and the car will idle but do a WOT run and take your foot off the gas with out in and see what happens.
Our IAC's are step motor versions. Their are 125 steps in which they can change the seat position. That is controled by the ecm with pulses to the iac and each pulse is 1 step. If the IAC dies it will stay at the last step it was at so If it died at wot it will be stuck at wide open which will cause the hanging idle if it died at idle it will be stuck midway which will cause stalling.
And Steve is exactly right when he said the IAC controls the dashpot.
Our IAC's are step motor versions. Their are 125 steps in which they can change the seat position. That is controled by the ecm with pulses to the iac and each pulse is 1 step. If the IAC dies it will stay at the last step it was at so If it died at wot it will be stuck at wide open which will cause the hanging idle if it died at idle it will be stuck midway which will cause stalling.
And Steve is exactly right when he said the IAC controls the dashpot.
I beg to differ, from the '03 factory shop manual:
Idle Air Control Valve
The idle air control (IAC) valve assembly (Figure 122) and (Figure 123) controls engine idle speed and provides a dashpot function. The IAC valve assembly meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body.
The PCM determines the desired idle speed or bypass air and signals the IAC valve assembly through a specified duty cycle. The IAC valve responds by positioning the IAC valve to control the amount of bypassed air.
The PCM monitors engine rpm and increases or decreases the IAC duty cycle in order to achieve the desired rpm. [emphasis aded]
On applications with air-assisted injectors, the IAC valve (Figure 124)also supplies a small amount of air into the path of the fuel injectors. The jet of air causes an increase in fuel atomization at low speed and light load conditions.
Note: The IAC Valve Assembly is NOT ADJUSTABLE and CANNOT BE CLEANED.
The IAC valve (part of throttle body assembly) has an internal diode on some applications. If the internal diode is measured in crossed terminal position with a digital multimeter, there will be an incorrect or negative reading. It is important that the mating component and harness connectors are correctly oriented. Diagnostic procedures emphasize this importance.
The PCM uses the IAC valve assembly to control:
The idle air control (IAC) valve assembly (Figure 122) and (Figure 123) controls engine idle speed and provides a dashpot function. The IAC valve assembly meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body.
The PCM determines the desired idle speed or bypass air and signals the IAC valve assembly through a specified duty cycle. The IAC valve responds by positioning the IAC valve to control the amount of bypassed air.
The PCM monitors engine rpm and increases or decreases the IAC duty cycle in order to achieve the desired rpm. [emphasis aded]
On applications with air-assisted injectors, the IAC valve (Figure 124)also supplies a small amount of air into the path of the fuel injectors. The jet of air causes an increase in fuel atomization at low speed and light load conditions.
Note: The IAC Valve Assembly is NOT ADJUSTABLE and CANNOT BE CLEANED.
The IAC valve (part of throttle body assembly) has an internal diode on some applications. If the internal diode is measured in crossed terminal position with a digital multimeter, there will be an incorrect or negative reading. It is important that the mating component and harness connectors are correctly oriented. Diagnostic procedures emphasize this importance.
The PCM uses the IAC valve assembly to control:
- No touch start
- Cold engine fast idle for rapid warm-up
- Idle (corrects for engine load)
- Stumble or stalling on deceleration (provides a dashpot function)
- Over-temperature idle boost.
- Air Assist to Injectors.
It is not a stepper motor...
Banned
Joined: Sep 2008
Posts: 0
From: tn
I don't know why I put "step motor" I ment to just put "step"
An idle air control valve is a three wire system. It consist of a five volt wire, a ground wire, and a sense wire. The five volt wire is used with the ground wire to move the IAC motor. The sense wire is a direct line for the computer to monitor how far in or out the valve is. The position of the valve in or out is know as steps. The IAC has a cone shaped tip called a pintle which protrudes into an air passage. The amount of air in this passage affects the engine idle speed. The pintle is on the end of a rod that has a spring around it. The rod is connected to the electrical motor which moves the rod and pintle in and out of a passageway. If the rod and pintle is pulled in by the IAC motor, the airflow is increased to raise the idle speed of the engine. The opposite will happen if the rod and pintle are pushed out. The airflow in the passage will decrease which in turn will lower the engine speed.
An idle air control valve is a three wire system. It consist of a five volt wire, a ground wire, and a sense wire. The five volt wire is used with the ground wire to move the IAC motor. The sense wire is a direct line for the computer to monitor how far in or out the valve is. The position of the valve in or out is know as steps. The IAC has a cone shaped tip called a pintle which protrudes into an air passage. The amount of air in this passage affects the engine idle speed. The pintle is on the end of a rod that has a spring around it. The rod is connected to the electrical motor which moves the rod and pintle in and out of a passageway. If the rod and pintle is pulled in by the IAC motor, the airflow is increased to raise the idle speed of the engine. The opposite will happen if the rod and pintle are pushed out. The airflow in the passage will decrease which in turn will lower the engine speed.
TECH SAVANT
Joined: Dec 2006
Posts: 10,937
From: Saint Augustine, FL
I don't know why I put "step motor" I ment to just put "step"
An idle air control valve is a three wire system. It consist of a five volt wire, a ground wire, and a sense wire. The five volt wire is used with the ground wire to move the IAC motor. The sense wire is a direct line for the computer to monitor how far in or out the valve is. The position of the valve in or out is know as steps. The IAC has a cone shaped tip called a pintle which protrudes into an air passage. The amount of air in this passage affects the engine idle speed. The pintle is on the end of a rod that has a spring around it. The rod is connected to the electrical motor which moves the rod and pintle in and out of a passageway. If the rod and pintle is pulled in by the IAC motor, the airflow is increased to raise the idle speed of the engine. The opposite will happen if the rod and pintle are pushed out. The airflow in the passage will decrease which in turn will lower the engine speed.
An idle air control valve is a three wire system. It consist of a five volt wire, a ground wire, and a sense wire. The five volt wire is used with the ground wire to move the IAC motor. The sense wire is a direct line for the computer to monitor how far in or out the valve is. The position of the valve in or out is know as steps. The IAC has a cone shaped tip called a pintle which protrudes into an air passage. The amount of air in this passage affects the engine idle speed. The pintle is on the end of a rod that has a spring around it. The rod is connected to the electrical motor which moves the rod and pintle in and out of a passageway. If the rod and pintle is pulled in by the IAC motor, the airflow is increased to raise the idle speed of the engine. The opposite will happen if the rod and pintle are pushed out. The airflow in the passage will decrease which in turn will lower the engine speed.
Ours is a 2-wire device as you can see from the wiring diagram snippet below, represented pictorially as a solenoid device--mostly 'cause that's what it is. It functions as described in my initial posting above.
3rd Gear Member
Joined: Aug 2008
Posts: 912
From: Oklahoma
I do not doubt that some IAC, on some engine somewhere, may indeed function in this manner. However the IAC on our 4.6L 2V engines does not.
Ours is a 2-wire device as you can see from the wiring diagram snippet below, represented pictorially as a solenoid device--mostly 'cause that's what it is. It functions as described in my initial posting above.
Ours is a 2-wire device as you can see from the wiring diagram snippet below, represented pictorially as a solenoid device--mostly 'cause that's what it is. It functions as described in my initial posting above.
Yep it has a duty cycle like you said, it opens and closes at different speeds, it’s not a servo that can open a little and stay there....
Funny story... I had an issue with my car idling really high and altering the tune did nothing, after 20 mins we decided it must be a bad IAC causing the issue, only to fine 1/2 a zip tie jamming the IAC open
TECH SAVANT
Joined: Dec 2006
Posts: 10,937
From: Saint Augustine, FL
The Internet is a wonderful thing, however as has been said* "it's like a herd of performing elephants with diarrhea...".
A bit of "googleing" revealed that the description of the 3-wire IAC posted above was taken nearly intact from this site, which also includes this brilliant statement:
Huh? The IAC and the MAF perform two completely different functions, their only connection being they both connect to the ECU.
One is an output/control device, the other an input/sensing device; the IAC cannot measure how much air is entering the engine, and the MAF cannot control same.
-----------------------------------
* - "Usenet is like a herd of performing elephants with diarrhea -- massive, difficult to redirect, awe-inspiring, entertaining, and a source of mind-boggling amounts of excrement when you least expect it."
-- -- Gene Spafford, 1992
Usenet is sort of the Internet's immediate predecessor...
A bit of "googleing" revealed that the description of the 3-wire IAC posted above was taken nearly intact from this site, which also includes this brilliant statement:
An idle air control valve is an electronic motor which adjust idle speed. The IAC valve is usually mounted to the throttle body. Some cars don't have IAC valves, instead they have a mass air flow sensor [emphasis added]. An IAC valve is used by the computer to change the amount of air flow
One is an output/control device, the other an input/sensing device; the IAC cannot measure how much air is entering the engine, and the MAF cannot control same.
-----------------------------------
* - "Usenet is like a herd of performing elephants with diarrhea -- massive, difficult to redirect, awe-inspiring, entertaining, and a source of mind-boggling amounts of excrement when you least expect it."
-- -- Gene Spafford, 1992
Usenet is sort of the Internet's immediate predecessor...
3rd Gear Member
Joined: Aug 2008
Posts: 912
From: Oklahoma
The Internet is a wonderful thing, however as has been said* "it's like a herd of performing elephants with diarrhea...".
A bit of "googleing" revealed that the description of the 3-wire IAC posted above was taken nearly intact from this site, which also includes this brilliant statement:
Huh? The IAC and the MAF perform two completely different functions, their only connection being they both connect to the ECU.
One is an output/control device, the other an input/sensing device; the IAC cannot measure how much air is entering the engine, and the MAF cannot control same.
-----------------------------------
* - "Usenet is like a herd of performing elephants with diarrhea -- massive, difficult to redirect, awe-inspiring, entertaining, and a source of mind-boggling amounts of excrement when you least expect it."
-- -- Gene Spafford, 1992
Usenet is sort of the Internet's immediate predecessor...
A bit of "googleing" revealed that the description of the 3-wire IAC posted above was taken nearly intact from this site, which also includes this brilliant statement:
Huh? The IAC and the MAF perform two completely different functions, their only connection being they both connect to the ECU.
One is an output/control device, the other an input/sensing device; the IAC cannot measure how much air is entering the engine, and the MAF cannot control same.
-----------------------------------
* - "Usenet is like a herd of performing elephants with diarrhea -- massive, difficult to redirect, awe-inspiring, entertaining, and a source of mind-boggling amounts of excrement when you least expect it."
-- -- Gene Spafford, 1992
Usenet is sort of the Internet's immediate predecessor...
5th Gear Member
Joined: Aug 2006
Posts: 2,158
From: Central NJ
ok so this is pissing me off, my stang will be fine on startup but a mile down the road if put it in neutral my rpms will be liek 2k sometimes 3k and when im at a stop its like 1500 rpms...i thot it was a bad IAC becuase when i unplugged the IAC and set my TB screw i had it idle normal and drive normally the check engine light just came on cuz it was unplugged, i replaced the IAC yesterday and the same thing is happening again...what could it be