IAC Technical Questions
10-03-2007, 07:14 PM
#1
2nd Gear Member
Thread Starter
Join Date: Apr 2007
Location: Detroit, Michigan
Posts: 208
IAC Technical Questions
Are the IACs for the 4.6s specific to each car, so, is it the IAC which determines the idle?, or is it the car's computer which determines the idle RPM?
Reason I ask, my old one seized shut, and I couldn't get it to come back to life with any consistency, so I raided the junkyard and pulled 2 off a pair of Mercury's with the 4.6. With either of them, my car idles at 1150RPM almost exactly, whereas it used to idle at almost 750RPM exactly.
Of course after a day, my car threw a "IAC Excessively High" code.
It would make more sense to me that the car would determine the idle RPM, do I just need to pull the battery to reset everything? (I ask without trying, cause I'm sick of resetting my stereo...)
Thanks!
Sub question, my stock one had a "7" engraved near the outlet passage, the 2 new ones had "13" and "15" engraved, what's this number represent?
Reason I ask, my old one seized shut, and I couldn't get it to come back to life with any consistency, so I raided the junkyard and pulled 2 off a pair of Mercury's with the 4.6. With either of them, my car idles at 1150RPM almost exactly, whereas it used to idle at almost 750RPM exactly.
Of course after a day, my car threw a "IAC Excessively High" code.
It would make more sense to me that the car would determine the idle RPM, do I just need to pull the battery to reset everything? (I ask without trying, cause I'm sick of resetting my stereo...)
Thanks!
Sub question, my stock one had a "7" engraved near the outlet passage, the 2 new ones had "13" and "15" engraved, what's this number represent?
10-03-2007, 08:29 PM
#2
5th Gear Member
Join Date: Aug 2005
Location: Whitehall, Michigan
Posts: 2,638
RE: IAC Technical Questions
ORIGINAL: aCiD
Are the IACs for the 4.6s specific to each car, so, is it the IAC which determines the idle?, or is it the car's computer which determines the idle RPM?
Reason I ask, my old one seized shut, and I couldn't get it to come back to life with any consistency, so I raided the junkyard and pulled 2 off a pair of Mercury's with the 4.6. With either of them, my car idles at 1150RPM almost exactly, whereas it used to idle at almost 750RPM exactly.
Of course after a day, my car threw a "IAC Excessively High" code.
It would make more sense to me that the car would determine the idle RPM, do I just need to pull the battery to reset everything? (I ask without trying, cause I'm sick of resetting my stereo...)
Thanks!
Sub question, my stock one had a "7" engraved near the outlet passage, the 2 new ones had "13" and "15" engraved, what's this number represent?
Are the IACs for the 4.6s specific to each car, so, is it the IAC which determines the idle?, or is it the car's computer which determines the idle RPM?
Reason I ask, my old one seized shut, and I couldn't get it to come back to life with any consistency, so I raided the junkyard and pulled 2 off a pair of Mercury's with the 4.6. With either of them, my car idles at 1150RPM almost exactly, whereas it used to idle at almost 750RPM exactly.
Of course after a day, my car threw a "IAC Excessively High" code.
It would make more sense to me that the car would determine the idle RPM, do I just need to pull the battery to reset everything? (I ask without trying, cause I'm sick of resetting my stereo...)
Thanks!
Sub question, my stock one had a "7" engraved near the outlet passage, the 2 new ones had "13" and "15" engraved, what's this number represent?
That'll force the ECU to open the IAC some to keep the idle up, and should stop the code from popping up (the code comes up when the ECU is trying to lower the idle further and can't by closing the IAC more).Try fabbing an IAC restrictor plate up using the instructions in the tech how-to's sticky here in the 4.6 section and let us know if that corrects the problem. You'll have to unplug the battery for a bit to clear out the code unless you want to drive out to AutoZone for it... it's probably easier (and better anyway) to just disconnect the battery while you make your IAC restrictor.
10-03-2007, 08:51 PM
#3
2nd Gear Member
Thread Starter
Join Date: Apr 2007
Location: Detroit, Michigan
Posts: 208
RE: IAC Technical Questions
I've already done that, and I have a code reader, so getting the codes out isn't a big deal...
So it IS the IAC which dictates the idle RPM? Or the car???
So it IS the IAC which dictates the idle RPM? Or the car???
10-03-2007, 10:48 PM
#4
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
RE: IAC Technical Questions
From the 2003 shop manual:[/align]
Because it's and electro-mechanical device, the IAC dampensthis varying duty cycle square wave and only opens "so far" to allow in a controlled quantity of meteredair (it probably pulses a bit in operation).
Did you reset the KAM (Keep Alive Memory) by disconnecting the battery for 5 to 7 minutes? This will force the PCM to relearn the idle trim settings...
Also from the manual:
[/align]
Idle Air Control Valve [/align]
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.
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.
Did you reset the KAM (Keep Alive Memory) by disconnecting the battery for 5 to 7 minutes? This will force the PCM to relearn the idle trim settings...
Also from the manual:
Idle Air Trim
Idle Air Trim is designed to adjust the Idle Air Control (IAC) calibration to correct for wear and aging of components. When engine conditions meet the learning requirement, the strategy monitors the engine and determines the values required for ideal idle calibration. The Idle Air Trim values are stored in a table for reference.
This table is used by the PCM as a correction factor when controlling idle speed. The table is stored in Keep Alive Random Access Memory (RAM) and retains the learned values even after the engine is shut off. A Diagnostic Trouble Code (DTC) is output if the Idle Air Trim has reached its learning limits.
Whenever an IAC component is replaced or cleaned or a service affecting idle is performed, it is recommended that Keep Alive RAM be cleared. This is necessary so the idle strategy does not use the previously learned Idle Air Trim values.
To clear Keep Alive RAM, refer to PCM Reset in Section 2 [ed: disconnect battery for > 5 minutes]. It is important to note that erasing DTCs with a scan tool does not reset the Idle Air Trim table.
Once Keep Alive RAM has been reset, the engine must idle for 15 minutes (actual time varies between strategies) to learn new idle air trim values. Idle quality will improve as the strategy adapts. Adaptation occurs in four separate modes. The modes are shown in the following table.
IDLE AIR TRIM LEARNING MODES
Transmission Range
Air Conditioning Mode
NEUTRAL
A/C ON
NEUTRAL
A/C OFF
DRIVE
A/C ON
DRIVE
A/C OFF
Idle Air Trim is designed to adjust the Idle Air Control (IAC) calibration to correct for wear and aging of components. When engine conditions meet the learning requirement, the strategy monitors the engine and determines the values required for ideal idle calibration. The Idle Air Trim values are stored in a table for reference.
This table is used by the PCM as a correction factor when controlling idle speed. The table is stored in Keep Alive Random Access Memory (RAM) and retains the learned values even after the engine is shut off. A Diagnostic Trouble Code (DTC) is output if the Idle Air Trim has reached its learning limits.
Whenever an IAC component is replaced or cleaned or a service affecting idle is performed, it is recommended that Keep Alive RAM be cleared. This is necessary so the idle strategy does not use the previously learned Idle Air Trim values.
To clear Keep Alive RAM, refer to PCM Reset in Section 2 [ed: disconnect battery for > 5 minutes]. It is important to note that erasing DTCs with a scan tool does not reset the Idle Air Trim table.
Once Keep Alive RAM has been reset, the engine must idle for 15 minutes (actual time varies between strategies) to learn new idle air trim values. Idle quality will improve as the strategy adapts. Adaptation occurs in four separate modes. The modes are shown in the following table.
IDLE AIR TRIM LEARNING MODES
Transmission Range
Air Conditioning Mode
NEUTRAL
A/C ON
NEUTRAL
A/C OFF
DRIVE
A/C ON
DRIVE
A/C OFF
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