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Doug
Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8538
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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Submitted: 1 year ago.
Category: Mitsubishi
Expert:  Doug replied 1 year ago.

Hi,

The switch from open loop to closed loop is completely normal and is no sign of anything wrong. The computer changes from closed loop to open loop as needed when it alternates between live data and fixed map fueling. Again, totally normal operation.

Is the primary problem that the idle is unusual/unstable?

Customer: replied 1 year ago.
quite unstable and rather low (almost killing the engine) when it is in open loop.
Expert:  Doug replied 1 year ago.

Thanks.

Again disregard the loop status, it should only be coincidental.

Please start the engine up and let it idle; if it is warm and having difficulty, slightly apply the gas pedal and try to get it to stabilize as low as you can/close to normal idle as you can.

In this state, turn the AC on and watch the tachometer (if you have a base model with no tach, listen to the engine). Does the engine go up slightly when you turn the AC on right before it kicks in, or does it remain level then go down slightly when the AC kicks in?

Customer: replied 1 year ago.
It goes up as the ac is coming on. The idle os erratic until I push it up over 1200rpm it smooths out after turning on the ac but then goes back to hunting between 800 and 200. Also I noticed when trying to mellow it out with the throttle is would just change rpms either up or down without moving the throttle.
Expert:  Doug replied 1 year ago.

Thanks.

Did anything noteworthy happen prior to this condition forming? Any repairs, maintenance, modification, etc?

Customer: replied 1 year ago.
That I would not know, I just purchased the vehicle, in this condition. I do not see any aftermarket add ons or anything of that nature. It does have 200K miles on it .
Expert:  Doug replied 1 year ago.

Thanks.
I'm most suspicious of the idle valve, simply because they are so common to fail on these. If you reach under the throttle body and unplug the idle valve (black six pin connector) and see if the behavior changes any.

Note this will usually turn your engine light on... that is OK for now.

Expert:  Doug replied 1 year ago.

I have to step out unexpectedly; I will be back as soon as possible.

Customer: replied 1 year ago.
Ok ill let you know about the idle valve
Customer: replied 1 year ago.
there seems to be no difference in the erratic idle with the idle valve unplugged at all the air conditioner is the only thing that makes much of a difference. The engine idles perfectly fine when the ac pump is engaged, but cycles back to hunting when the pump cycles off. It's almost like it doesn't care to run without a load.
Customer: replied 1 year ago.
Also if I release the clutch and coast at idle speed down the road the idle os smooth as well. It really only hunts with no load on engine.
Expert:  Doug replied 1 year ago.

I apologize for that delay, I had an unexpected problem I had to address.

Before doing anything else.... lets take the intake duct off carefully then take a rag and soak the rag liberally with brake parts cleaner or other evaporating solvent. Take the rag in your right hand, and twist the throttle open with your left hand, then reach in and wipe out the throttle body thoroughly. The sealing area where the throttle plate rests when closed needs to be spotless... no brown or black deposits at all. If you have hard deposits you can use a scotch brite pad or wire brush to help knock them loose, then wipe out again. When done you should see nothing but silver in there... then reconnect the intake hose and see if we affected the situation positively.