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sprinkles08
sprinkles08, ASE Certified Technician
Category: Car
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Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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Pajero 2003 6g72 iac solenoid problem

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pajero 2003 6g72 iac solenoid problem

Hello and welcome to Justanswer!

If the IAC motor isn't working it could be due to the motor itself, wiring, or failed drivers within the engine controller. The IAC itself would be most likely.

What is the actual problem you're trying to diagnose?

Customer: replied 8 months ago.
hi
the engine wouldnt idle as it used to, neither in gear nor with ac turned on... apparently iac solenoid is not receiving the right signal even after swapping it with a known working unit.im just trying to figure out what other sensors/connections that might be at fault or responsible for this failure...
i recently changed injectors on the engine but one wasnt working and the engine ran on only 5 cylinders for almost 20KM....ive swapped back the faulty injector and everything runs fine except for the iac now...
Have you checked for fault codes?
Customer: replied 8 months ago.
no i havent... but ive disconnected the battery for more than an hour in attempt to clear any trouble codes and see if the issue might reset to normal. that didnt do me any good. the iac was running fine prior to the injector replacement job...
i dont get any check engine light btw... im just wondering what other input signals 'from other sensors around might have a hand in this issue if any... my worry is that something might have gone wrong in the ecu while the engine was limping on 5 cyl only... other than that the engine runs smooth with no other electrical issues at all...

Disconnecting the battery is counterproductive because it will clear fault codes necessary to diagnose the problem, and it will cause the engine controller to lose it's IAC memory. Disconnecting the battery is guaranteed to cause idle issues until the IAC counter relearns. Do you have scan tool to do an idle relearn?

Customer: replied 8 months ago.
unfortunately no scan tool at hand... could we narrow down some possible causes for this issue please?
ive changed my spark plugs several times previously and had the manifold in and out without facing this problem...
any ideas to what might have caused this? as i said the iac is not getting any signal no change with or without its harness connected... is there a specific voltage or resistance that i can check for at harness side? i know two middle pins are positive 12V and have verified that voltage is present there against ground already... also the solenoid checks out on resistance across terminals...

How do you know the IAC isn't receiving 'signal'?

Customer: replied 8 months ago.
simply because the idaling is not right and not compeensating when in gear or when ac is on. and car wont start without pressing the gas pedal and keeping the rpms high manually for some time.
ive removed the iac solenoid from the manifold and the spindle will not chamge position when ignition is turned on it only vibrates a bit in place
Customer: replied 8 months ago.
could i please be reftred to Doug!?
as he had helped me in the past and im already used to his diagnosis.
thank you

If it's vibrating when the key is turned on then the drivers are present, the IAC has mechanically failed if it vibrates and does not move. After it's replaced a scan tool is going to need to be used to do an idle relearn.

Customer: replied 8 months ago.
thank you. but i would still prefer to proceed with Doug please

Your question was open for an extended time and seen by all automotive experts, none of which were willing or able to help.

Customer: replied 8 months ago.
even Doug?
thats strange!

He, as with all others that passed over, either was not active at the time the question was open or did not feel that he could help for whatever reason.

Customer: replied 8 months ago.
could we please try again with Doug?
pleaee accept my appologies but i intend to figure out whats going wgith this iac befoe getting ripped off at the dealer. and im quite sure that thete is no need for a scanner callibration for the idle. it should have idled high fro some time before it self learns again the proper idle. in my casr there is no idle air comtro whatsoever rms are as low as 600 from start!

I will open your question for others to see if someone else will respond.

Customer: replied 8 months ago.
no one out there is capable of answering my question yet?!

I am fully capable of answering your question and did so correctly. I have nearly 20 years dealer experience and am very familiar with the 3.0 Mitsubishi engine.

You requested Doug only hence the lack of another response. From what I can see it appears Doug has only answered one question since October.

Customer: replied 8 months ago.
i have no doubt in your expertise sir..
so lets try again if u dont mind.
could we do a diagnosis of the issue here?
im only trying to narrow down the causes hoping that we might find the main source of this fault...
the way i see it, is that the ecu is either not receiving a command to operate the iac solenoid when needed due to some input sensor failure, or its not sending the right signal back to the iac itself... could we please elaborate on this matter or any other aspects that you might find worth investigating. as i said the engine runs smooth and no other apparent electronic faults that i have noticed yet... everything seems to be operational as it should be except that iac...

We did diagnose the issue. If the IAC is vibrating and not moving then it has failed. It's locked up mechanically.

Customer: replied 8 months ago.
but i replaced that unit already with a known working unit...

That wasn't mentioned previously.

How did you determine it was a working unit?

Customer: replied 8 months ago.
the resistance across the leads check out fine
Customer: replied 8 months ago.
the previous unit was also fine apparently... both middle pins to outer pins have resistence each side in turn

Checking resistance of the motor driver circuits doesn't mean that the IAC is good, only that the motor circuits are complete. Is that what you did that you believed told you the replacement was good?

Customer: replied 8 months ago.
well yes
as far as i know these are very basic solenoids... not much to test appart from the right ohm across the pins... i even disassembled the unit and have managed to verify that the inner bearings are free and the core screw spins perfectly fine
Customer: replied 8 months ago.
could we please consider other possibilities?
harness side, input sensors, fuses anything else that might be involved here

It's a stepper motor rather than a solenoid.

To know it's a functional unit you need to see it operating correctly on another vehicle. If that has not been done it is not a known good part. I have little reason to doubt the problem is the IAC if it vibrates and doesn't move. Its either the IAC or a poor driver as I mentioned before.

You either need to replace the IAC with a new part from a dealer concentrate on testing the wiring and ECM. You can load test the IAC drivers from the ECM to the IAC. If ok then the next step would be to use a scan tool to actuate the drivers and if ok then you're back to needing an IAC.

Customer: replied 8 months ago.
theres a possibility that the drivers on the ecm side have failed due to the clogged fuel injector i had?
if so, i just wonder how come all other functions of the ecm are still intact...
not even a check engine light came on...

The problem is not related to the injector.

If no fault codes are setting then there should not be a wiring or ECM issue but it's possible.

Customer: replied 8 months ago.
i mentioned the injector cause this only happened after i changed injectors and one of them turned out to be faulty leaving the engine to work on 5 cyl only... i kept driving the car like that for over 20miles... only after this episode the iac stopped working...

Unless you damaged the IAC or wiring this is not related to the injector.

Customer: replied 8 months ago.
all was working fine before that...
the battery positive lead got shorted on to the engine manifold while it was running for a split of a second... could that have done any electrical damage?

Absolutely, that will instantly damage any electrical component.

Customer: replied 8 months ago.
but the short was straight to ground via engine body right?
could it have spiked down to the ecm?

Yes, any electrical component including the ECM can be damaged by shorting power to ground or reversed polarity.

Customer: replied 8 months ago.
alright
so is there a way to test for ecm harness side failure at iac plug?
there are 6 pins two of wich are in the centre and are positive 12V
any idea what the remaining outer pins should read? in volts or in ohm?

You'd need to locate the wires at the ECM and load test them with a headlamp or fog lamp bulb making sure the bulb lights as brightly as if connected to the battery.

Customer: replied 8 months ago.
ok...
bulb goes from centre pin across to both side pins in turn?
bulb should light brigh upon switching ignition?

You'd disconnect the IAC and ECM. Connect a jumper wire from battery positive to one terminal on the bulb and a second jumper wire from the second bulb terminal to the wire you're testing at the IAC connector. At the ECM end you'll connect a jumper wire from the wire you're testing to ground to see if the bulb lights.

Customer: replied 8 months ago.
buddy im not testing for wire integrity here...
my question was how to test driver signal from the ecm itself via the harness!!
is there a volts or ohm value that i should look for there?

You'd need a scan tool for that, and if a driver wasn't present then you'd need to test the wiring as described before being able to condemn the ECM.

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