Help with idle issues

[Dmenz929]

Looking for some help with diagnosing my 02 pathfinder. I have been a long time lurker of this forum but this is my first time posting. My pathfinder had a problem with the idle jumping from 1500 rpms to 2k. Switched the iacv now it is stuck in the fully open position and idles at 400 rpms and dies. I had recently replaced the injectors with fbjc101 injectors changed all the intake manifold gaskets. After it drove great for over 6 hours. Then the idle problem started. I have taken out the pcm and the idle air circuit isnt burned looking or smelling. My main questions are could the pcm be bad even without evidence of it being burnt , or is my problem a vacuum leak from a problem with the intake. I cannot hear any hissing nor seen any smoke when I did the youtube cigar smoke test. Thanks for any help.

[VStar650CL]

Unless it's huge, a vacuum leak will typically increase the idle and not decrease it. That's the principle the IACV works on, so one that's stuck open should cause a high-and-uneven idle and not a stall. Stuck shut might cause the symptoms you're seeing.

The IACV itself is a unipolar stepper motor that only draws about half an amp per phase, so yes, it's entirely possible to blow up the driver chip with no smoke or external evidence. Shorting either of the two power poles to any of the four phase wires will blow that phase in the IC as soon as it tries to operate. IIRC the chips used employed darlington BJT's and not FET's, and overloaded BJT's usually blow open and not short. That means you won't generally get blisters in the epoxy like you would from a melted MOSFET.

[Dmenz929]

Thanks for the reply I have the mec14-346 pcm I have heard the mec14-345 pcm is compaitable with my pathfinder. Do you know if that is true?

[VStar650CL]

No idea, sorry. Those are Hitachi part numbers, and Nissan has never published anything to cross reference the Hitachi numbers with Nissan p/n's.