The Autonerdz Community Forums - Intake Air Stepper Motor question

James H

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Intake Air Stepper Motor question
Jun 15^th, 2017 at 4:37pm

I have a fuel injected bike with a very high idle problem...5,000 rpm. It does not have a TPS, only map. ET, IAT, and O2 sensor. I have verified the temp and map sensors are good. There is a 4 wire Intake air stepper motor that functions but appears to be backwards. That is, it is closed with the key off and fully open with the key on. When you start the bike is stays in a mostly open position. There is no scan tool for this so I have no help there. You can get the bike to idle down if you manually plugged the air port. I voltage dropped all 4 wires and they are good. The ECU appears to command the stepper as you can see in the waveform (see cloud under my name GT250) but I not sure if what I am seeing is correct. I would appreciate any input before I condemn anything.

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Mick LSD Guide Offline I learn every day Posts: 7,471 Toronto 400ft Ontario Canada Gender:	Re: Intake Air Stepper Motor question Reply #1 - Jun 15^th, 2017 at 6:04pm James H wrote on Jun 15^th, 2017 at 4:37pm: I would appreciate any input before I condemn anything. Cars and truck mostly work off battery voltage for IAC valves. Is it normal for bikes to only have 9V to operate them? Have you thought about looking and each pair with an Amp clamp?
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Re: Intake Air Stepper Motor question
Reply #2 - Jun 15^th, 2017 at 7:56pm

James H wrote on Jun 15^th, 2017 at 4:37pm:

I have a fuel injected bike with a very high idle problem...5,000 rpm. It does not have a TPS, only map. ET, IAT, and O2 sensor. I have verified the temp and map sensors are good. There is a 4 wire Intake air stepper motor that functions but appears to be backwards. That is, it is closed with the key off and fully open with the key on. When you start the bike is stays in a mostly open position. There is no scan tool for this so I have no help there. You can get the bike to idle down if you manually plugged the air port. I voltage dropped all 4 wires and they are good. The ECU appears to command the stepper as you can see in the waveform (see cloud under my name GT250) but I not sure if what I am seeing is correct. I would appreciate any input before I condemn anything.

Got to this late so first thought off the top of my head is how the PCM interprets its' inputs to as you feel command the IAC to that high of a rpm.

When you plug the port and the rpm's come down what happens when you then unplug the hole? Does the rpm stay down or start climbing back up?

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N.B.S. Dilly Dilly! FJB

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James H Senior Member Picogroup Offline Bike Nerd Posts: 165 Waterloo Ontario Canada Gender:	Re: Intake Air Stepper Motor question Reply #3 - Jun 16^th, 2017 at 2:22am I knew I'd get nailed on the battery voltage. This was after I had done a bunch of previous checks and the battery was getting run down. I had checked this earlier when voltage was good ( and didn't save the capture) and the waveform looked the same. The revs do immediately climb back up after unplugging the port.
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James H Senior Member Picogroup Offline Bike Nerd Posts: 165 Waterloo Ontario Canada Gender:	Re: Intake Air Stepper Motor question Reply #4 - Jul 24^th, 2017 at 4:00pm Update. Thought I would give an update. It was the ECU causing the issue.
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