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Discussion Starter · #1 ·
What does the ECM need to see in order to make the IAC motor operate.

TPS is in idle and RPM signal???

I ask because when I turn the car off I hear the distinct 4 clicks coming from the motor. I checked resistance on the actual motor and it seems to work fine. I removed the motor from the flange covered the flange inlet and moved the accelerator through a range of 50% to closed throttle. I see the pintle moving to eliminate stall when going from open throttle to slammed shut.

But I have no idle control, I started with the stop plate screw backed all the way out. TPS adjusted so E1 or E2 and IDL show continuity with a .021 feeler guage and going to OFL with a .028 feeler guage. With these settings and the IAC motors range of 124 different positions I would expect at cold start the car would start with no throttle input. It would have an elevated RPM and eventually drop down once a certain ECT reading was achieved. This is not the case. Would the forum agree I should be able to have the stop plate screw backed all the way out and the 124 positions IAC motor should allow the car to start. It should recognize RPMS are not where they should be and the ECM should adjust the pintle to introduce more air into the engine and voila crank / start / run.


I adjusted the stop plate screw to allow the car to start on it's own with no throttle input. I adjusted the TPS sensor accordingly and waited for it to warm up so the ECM could tell the pintle to reduce air flow through the IAC assembly. The idle remained high?

My assumptions are the ECM is looking to maintain an idle of 750 rpm +/- what 50 rpm. If it doesn't see this once it's gone through it 's warm up circuit it would start adjusting the IAC pintle does anyone know if this is the case.

I have checked for vacuum leaks, there are none. Afterall the car won't start without throttle input if the stop plate set screw is backed all the way out. If there were leaks I would think it woudl fire up and I would have a high idle issue.

Any ideas.
 

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The IACV is activated by the TPS. When the throttle closes is completes the circuit that activates the IACV. The computer then looks at the RPM signal and tries to get it to 700rpms +/1 50rpms. If your TPS IACV switch is bad the IACV will not activate so if it is fully closed your car more than likely won't idle, or if it does, it will idle very low. If the IACV is open then your car will idle very high.

My TPS was messed up and the IACV was fully open. The car idled at 1600rpms. ONce I fixed the TPS by calibrating it, the IACV became active and the idle resumed correctly.

Your problem sounds like even though the TPS is shows continuity when closed, it isn't completing the circuit. This could be an ECU problem.


Steve
 

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Discussion Starter · #3 ·
Your problem sounds like even though the TPS is shows continuity when closed, it isn't completing the circuit. This could be an ECU problem.


Steve
Makes sense I'll look into the procedure for testing what the ECU is seeing.

Do you happen to know what the ECU looks for RPM wise on cold start idle and at what temperature it pulls the idle back down to the 700rpm?
 

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Hi I know this is an old post but I’m having the same exact problem. Just curious if a new ecu solved your problems?
 

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Bumping this up. I had a perpetual high idle for a long time (1100RPM), except for rare cases where it would drop to 700. Idle setting on the TB is 100% stock, nothing fiddled with.

I finally took the IAC apart and cleaned it, it wasn't that dirty. I then ground each terminal per the FSM, and it moved each time, but I had to have my thumb on it to "feel" it move, because the movement was barely perceptible to the eye.

Now that it is back on the car, it is not working at all, car will not stay running w/o throttle input. It does not click after shutting the car off, and it doesn't bump up idle for the A/C. Is there a certain position you need to leave it after you ground each terminal? Are there really 124 different positions?

Also, I could have sworn when I first took it off that the plunger was farther open than it is now. I should have taken a pic. It is currently not open much at all.

Thanks,
Al
 

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Sounds like it’s not getting power now. With the engine running give the wiring wiggle test. See if there’s any change. It’s possible the iac was on its last leg before you removed it and it shit the bed while being handled.
 

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Actually, the IAC is fine. I took it off and bumped it open 4 more steps, and now the car idles great.

It appears that if you run it thru the tests, you need to open and shut the valve the same number of steps to put it back the same as it was. In my case, it was closed a lot farther than when I first took it off, not allowing the car to hold an idle. Of course, it will adjust over time, but evidently will not start if set too low.

Al
 

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Okay, it was idling at 850, occasionally dropping to the proper 650-700 if it's in a good mood, or after 30 min of driving, whichever comes first. I verified all the throttle body settings except the TPS.

UPDATE: starting it up on a really cold morning, it's idling back at 1200 RPM again! Idle is smooth, just too high. The IAC works, just won't hold the proper idle speed. Anyone have a new IAC fix an issue like that?

Thanks,
Al
 
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