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Thread: '94 4G64 idle issues

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    Status
    Offline
    Join Date
    01-27-2021
    Posts
    21
    Location

    North Carolina
    Vehicle

    1994 Mitsubishi Mighty Max
    Engine

    4G64

    Question '94 4G64 idle issues

    Hello All! I'm wrestling with some funky idle issues on my '94 4G64 MM and hoping someone will know what's going on. Here's what the truck is doing:

    - I started noticing idle issues when the AC was running, where the truck would idle down very low and almost felt like it would stall out. This got me wondering about the idle control solenoid and the problem continued to get more noticeable over the course of a few weeks.
    - Without the AC running, sometimes the truck would idle way up. Sometimes, it would pulsate and rev up and down at idle.
    - Apart from the idle issues, the truck runs just great. Plenty of power and revs up normally.

    So, I tested the ohms on the idle control and it was outside the range in my manual. Not waaaaaay outside but I enough that I thought maybe that was the problem. I found a good used unit and put that in but I'm still having idle problems.

    I tested the ohms on the throttle position sensor and it's in spec so I'm not suspicious there.

    Edit - Forgot to mention that I cleaned the MAF with MAF cleaner, it looked spotless already and there was no change afterward.

    I went to start the truck yesterday and heard a click from behind the glove box (this is a US-spec truck) and absolutely everything electrical stopped working. Interior lights, the whole deal. Disconnected and reconnected the battery and it came back. Huh...

    This morning I pulled the glove box to listen for that relay and look for anything out of sorts. I can hear it popping open and closed and the truck started up fine. At first, it idled normally. Here's what has me puzzled. When I closed the passenger side door (not super gentle but not slamming it either), the truck immediately idled up high. I know the ECU is sitting right on the other side of that door hinge, is it possible that the ECU is the source of the issues here and the impact of closing the door made a difference?

    It looks like a pain to pull and rather than cross my fingers and fire the parts cannon again, I figured I'd check with the experts here.

    The original owner kept service records and the original ECU was replaced at a Mitsu dealer in 2007, about 27k miles ago. What do you all think, are these symptoms of ECU issues or am I headed in the wrong direction?
    Last edited by doots; 10-09-2022 at 02:48 PM.

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