I'm new here. Hello. Been looking and found a few things about this problem but I have not really seen many answers. Sorry if I am repeating stuff. Please point me in the right direction if I am missing something.

I just purchased a 1990 Montero RS. Starts and runs but the idle sits around 2500 rpm. The folks before me replaced the idle stepper motor. I checked the IAC valve and it is within specs. Checked the harness and it is good. Cleaned the throttle body. All seems normal.

When I unplug the Mass Air Flow sensor the engine idle drops down to around 600. Cleaned the Mass Air Flow Sensor. (new one is $720???)

I've read about resetting the ECM and seems like a pretty strange process. I'll try it but sounds a bit wonky. I see in my vehicle the ECM was replace at one point.

Any thoughts? Thanks for any ideas.

Excited about my new purchase. Always loved the boxy body style of the Montero.

 

I know that this is an old thread, but I thought I'd respond to it for anyone else who's potentially facing this issue (as I was). The Gen1 6G72 3.0l V6 has a Fast Idle Air Valve (FAIV) that sometimes gets stuck open or fails outright. There are replacements available from the major parts shops, but they're expensive (almost $300). You can try disassembling the valve and cleaning it, or adjusting it so that it is always closed, or use a bypass kit (sold for the 3si guys by Ninja Performance I think). But this is usually the reason for high/fast idle and/or lean condition that can't be adjusted out by the idle screw or base idle air screw.