IAC motor question
08-15-2012, 07:55 PM
#1
IAC motor question Upon receiving my ECM from a mailorder tune, the instructions asked that the throttle blade be set so that the counts would register between 40 & 60.
AutoTap is showing a constant reading of zero counts, no matter how the throttle blade is adjusted. Also, there is no vacuum leak. I've tested this with propane, starter fluid, & then a smoke unit.
I borrowed an Actron unit, and IAC doesn't even show on the menu.
Then it occurred to me that there are 4 wires on the IAC.
My question(s) are/is, would there be two pairs of wires...one pair (batt & grnd) to operate the IAC pintle outward, then another pair (batt & grnd) to retract the pintle? If this is true, then it would follow that one cannot read idle air counts directly. There would be no wired return to the ECM.
On another thread, someone mentioned setting the throttle blade by checking the TPS degree.
Comments on how to verify idle air counts...do I need some other type of diagnostic to do this?
Thanks.
AutoTap is showing a constant reading of zero counts, no matter how the throttle blade is adjusted. Also, there is no vacuum leak. I've tested this with propane, starter fluid, & then a smoke unit.
I borrowed an Actron unit, and IAC doesn't even show on the menu.
Then it occurred to me that there are 4 wires on the IAC.
My question(s) are/is, would there be two pairs of wires...one pair (batt & grnd) to operate the IAC pintle outward, then another pair (batt & grnd) to retract the pintle? If this is true, then it would follow that one cannot read idle air counts directly. There would be no wired return to the ECM.
On another thread, someone mentioned setting the throttle blade by checking the TPS degree.
Comments on how to verify idle air counts...do I need some other type of diagnostic to do this?
Thanks.
08-15-2012, 08:25 PM
#2
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,605
Likes: 0
Received 6 Likes
on
6 Posts
The IAC is a stepper motor and has a 4-phase set of drive
signals.
Now some PCMs omit the IAC driver circuitry. If so then you
will see nothing on the pins. Otherwise there should be some
averaged voltage from any given IAC pin to GND. I recall like
50-100mV on the meter. We were surprised by this on a
Frankenstein truck setup when we tried to use the stock
DBW PCM with a cable/IAC throttle.
If you have excess bypass air and are running above the
set idle RPM then the IAC will drive down to zero counts.
Test by commanding a higher idle, or use bidirectional
controls (scan tool) to manually set an IAC count and
see whether this controls RPM.
signals.
Now some PCMs omit the IAC driver circuitry. If so then you
will see nothing on the pins. Otherwise there should be some
averaged voltage from any given IAC pin to GND. I recall like
50-100mV on the meter. We were surprised by this on a
Frankenstein truck setup when we tried to use the stock
DBW PCM with a cable/IAC throttle.
If you have excess bypass air and are running above the
set idle RPM then the IAC will drive down to zero counts.
Test by commanding a higher idle, or use bidirectional
controls (scan tool) to manually set an IAC count and
see whether this controls RPM.
08-23-2012, 09:55 AM
#3
I've located my CD/manual, and checked the schematic for this.
Of the four wires connected to the IAC, two of them operate the motor toward closed position. The other two wires operate the IAC toward the open position.
There is no way to know at what position the counts are set @ the IAC, unless there is a method to know how many counts the computer is asking for.
Even then, it is not a verification of the actual IAC position.
Of the four wires connected to the IAC, two of them operate the motor toward closed position. The other two wires operate the IAC toward the open position.
There is no way to know at what position the counts are set @ the IAC, unless there is a method to know how many counts the computer is asking for.
Even then, it is not a verification of the actual IAC position.
