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Mitsubishi Repair/High Idle / Poor Mileage


charlierzz wrote at 2011-08-03 22:08:14
Also can try the idle control needle screw on top of the TB

amitsuman wrote at 2013-06-15 15:35:27
This guy is not a mitsubishi owner. If he had a montero of his own, he may understand your high idle concern. BE concerned. Mine finally grew to 2200rmps  a month ago and just this week... NOT coming down anymore. I rode out the increase in startup rpms for 4 yrs and now there is no normalization. This week marks the beginning of having to sort this problem out. Chillin at a stoplight @ 2200 rpms so ridiculous.  

amitsuman wrote at 2013-06-15 16:54:09
I'm gonna try the fiav valve check/replace. I heard a mitsu person say this fixed their high idle start up issue. I hope it solves mine. Will give a heads up when i do. It could be a month... good luck.  here's what was said about it... (It sounds reasonably close to the prob)

1). there is a valve in a car that makes them run at a high idle when ata cold start. Its called the Fast Idle Air Valve (FIAV). What it does is have the engine rev higher during a cold start to warm it up faster. Perfectly normal


2). I would say its the fiav. They make a block off plate which lets you keep your ISC motor. As the engine warms up its supposed to close, not letting as much air bypass the throttle plate (its a simple thermostat). Yours seems stuck open, letting air continue to bypass the throttle. You might want to check the throttle shaft seals as well. I had this same problem, but to fix it I went a little over board. I replaced the throttle body gaskets, the BISS screw and o-ring, the throttle shaft seals, and put in the FIAV block off plate. My idle is perfect now. however, without the FIAV, its a little choppy if its a cold morning. If its warm though its perfect

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Anthony Falcone


I have been working with (and driving) a first generation Mitsubishi Eclipse for several years. Anything that could go wrong with an Eclipse has probably happened on mine. Fortunately, I have gained a lot of knowledge from experience in repairing these problems myself.


Identifying and repairing problems in mechanical and electrical areas. Plus, I have learned many ways to enhance performance to the incredible engine Mitsubishi put in their early model Turbos.

AS degree in Engineering Science
BS degree in Electrical Engineering

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