Toyota Idle air control PCM control?

Hello,

Vehicle is a UK spec '99 Toyota Rav4. Vehicle is running lean and during the process of elimination I checked the 3 wire idle air control valve and found that the ISCO (open) valve (yellow/black) wire was giving a signal on my scope and the duty cycle was at 40%. However, checking the ISCC (closed) valve (blue/black) gave no scope signal whatsoever. Rechecked connection, all good but still no signal. The idle air control is ground side switched with power coming from a relay.

Can I test for PCM control at the idle air control valve by back probing the blue/black ISCC wire with a test light connected to battery positive?

Thanks for any advice

Stephen

Since it is duty cycled, I, myself, am not comfortable back probing and completing the circuit a duty cycled actuator. This is because you would keep it at 100% duty cycle for probably more than designed. IMHO, at 100% duty cycle, this allows a good amount of current through the IAC and would most likely damage it due to the heat generated.

I'm sure there is someone more comfortable doing this. Again, for me, not so much. I don't recall any ScannerDanner videos where he does this. From memory, he uses a scan tool to view IAC duty cycle PID and control it.

I suggest watching a ScannerDanner video named "Toyota 3-wire solenoid type IAC Waveform." The two control wires should add up to 100% in regards to duty cycle. Since, one was at 40%, the other control wire should have been very close to 60%.

How I test and work with the IAC is through bi-directional control on my scan tool and run it through a variety of duty cycles. Another option is to use a scan tool to view the IAC duty cycle PID and turn on engine load at idle, A/C, Lights, Stereo, cabin vent blowers on high. This increases alternator load which in turn causes the idle RPM to increase by the IAC opening up.

Did this help at all?

Thanks for replying. Good points raised. One of my problems is being UK specification it only has OBD1 so unfortunately i cannot use a scan tool.

toyota1990s wrote: Hello,

Vehicle is a UK spec '99 Toyota Rav4. Vehicle is running lean and during the process of elimination I checked the 3 wire idle air control valve and found that the ISCO (open) valve (yellow/black) wire was giving a signal on my scope and the duty cycle was at 40%. However, checking the ISCC (closed) valve (blue/black) gave no scope signal whatsoever. Rechecked connection, all good but still no signal. The idle air control is ground side switched with power coming from a relay.

Can I test for PCM control at the idle air control valve by back probing the blue/black ISCC wire with a test light connected to battery positive?

Thanks for any advice

Stephen

Yes you can. But I would use an LED test light here. I have found some of these IAC valves using very low current pulses (40-50 ma). I'm sure an incandescent light would work but why take a chance on too high of current.

So to be clear. The wiring on this IAC.
1. constant battery feed
2. IAC control (ground side switched)
3. IAC control (ground side switched)

These two controls should mirror each other. When one is high the other is low.
Here are two pictures from my book Chapter 20 "Idle Speed Controls"





If this is what you are dealing with, what voltage does your scope show you on the no control circuit? Is it fixed at 12 or 0 volts?

Thanks for replying Paul.

You are correct about the wiring on this idle air control valve and it is identical to page 25 in your book.

Voltage on the scope is fixed at 0 volts on the no control circuit.

Thanks

Stephen

toyota1990s wrote: Thanks for replying Paul.

You are correct about the wiring on this idle air control valve and it is identical to page 25 in your book.

Voltage on the scope is fixed at 0 volts on the no control circuit.

Thanks

Stephen

Okay cool. So with a ground side switched output fixed a 0v. Here are your options:
1. No feed voltage (not a problem here as the other coil is working and it is a shared feed)
2. Open coil winding in the IAC
3. Short to ground on IAC control wire
4. Shorted ECM driver

THE test to do here is with a test light connected to battery positive and touch on the control circuit that is not working.
Report your results of this test. I would first do it with the valve plugged in and backprobing, then depending on the results, I may want to unplug the IAC and redo the test.

If the driver has the ability to pulse the test light on/off, then your wiring and computer is good, replace the solenoid

Thanks for taking the time to reply Paul.

Can this test be carried out with a LED logic probe that is connected to battery positive and battery negative?

If not i can soon get a proper LED test light.

The logic probe should be okay. I would maybe like to see a little more load than that though. And LED test light is around 12-20 ma. Any idea what the amperage is of that logic probe?

35 ma on the literature Paul

Then you should be good with that. Let us know what the result is.

I tested the non working control wire using the logic probe and both the green and red LED lights lit up together, they did not flash but stayed lit at the same time.

Interesting. But you said when you scoped it, you saw no control on this wire. Right?

I rechecked my scope and it is now giving a signal. I believe when I originally back probed the control wire on the IAC I placed the pin at the side of the control wire away from the adjoining feed wire. I did check that the pin was all the way in but I can only think it must have slipped past the contact point. When I back probed the control wire using the logic probe I remember that I inserted the pin to go beneath the wire as opposed to beside the wire and suddenly I got a signal.

User error is to blame but on the plus side I did not buy any replacement parts and have not caused any damage. I feel a little foolish but I'll learn from my mistake.

Thank you Paul and GeekDIYmechanic for all your help. Much appreciated.

Stephen