94 Montero - Engine suddenly will not Idle
 

Greetings Hunter and all. The following is probably a simple issue for some of you to diagnose. I thought I would run it by here before I start tackling the issue:

1994 Montero SR. Has been running perfectly for the past year, "per-fect-a-mente'", like a new one. A couple days ago, I started her up and she stalled and cut off when I tried backing her out. I could re-start w/o any issues, but have to keep my foot on the gas a bit so the RPMs dont go way down which causes the engine to cut-off. So, there is a Idling Issue----where it used to idle nicely at around 6-700 RPMs, now it will just drop below this and die out. I can rev the engine up and it seems fine, but just will not hold an Idle. 3/4 tank of gas, and the fuel filter replaced less than 1000 miles ago.

My first thought was maybe a fuse or breaker that controls the MAF sensor or maybe the Throttle Body butterfly flap was dirty. However, I am pretty certain that I cleaned both less than 1000 miles ago.

Note: I had a small trickle charger on the battery for about a week before this issue started. Could the battery have been a bit over-charged and sent a surge to one of the fuses?

Any reccomendations would be appreciated.


https://cimg0.ibsrv.net/gimg/mitsubi...f15044901d.jpg


https://cimg2.ibsrv.net/gimg/mitsubi...b0bd649a52.jpg

I would look into replacing the idle air control valve if you haven't already, if this becomes faulty it will cause a rough idle or won't idle at all. you could also try cleaning the IAC gently and see if that was the issue.

I second the possibility of the idle control valve not working properly. Another possibility is a stuck open EGR valve (if your engine has one).

Naeos & Hunter.......Thanks for the reply/suggestion. (I never got an email notification, so I did not know you replied.....my bad). Thats a huge help......I found a Youtube video from Ratchets and Wrenches, and he did a perfect video on the Mitsu. Montero on how to replace/clean the IAC. I will give it a shot tomorrow, and will order a couple IACs to have on hand.
Thanks a million.
Here is the youtube video from Ratchets and Wrenches:

Here is a pic of the Idle Air Control, seen unplugged in the pic:

https://cimg1.ibsrv.net/gimg/mitsubi...f389463ba0.jpg

This was an original OEM Mitsubishi part, and did have a fair amount of grime on it:


https://cimg2.ibsrv.net/gimg/mitsubi...2deed24c98.jpg

Also corrosion on the inside where it mounts:


https://cimg6.ibsrv.net/gimg/mitsubi...af15782d4b.jpg



https://cimg1.ibsrv.net/gimg/mitsubi...ba5f8cf86a.jpg

Cleaned it up, along with all the corrosion in the mount area, and re-installed it to see if it would work. Nope.......engine would start up fine, but would not idle.....would just drop RPMS down to 0 and stall out.

https://cimg7.ibsrv.net/gimg/mitsubi...63da718c81.jpg

Continued.

The price for an OEM Mitsu. brand part is crazy high.....3-400 bucks. Rock Auto had knock-off brands for $50. I forgot to check eBay, and sure enough, I just found the same part for less than $20 on eBay. Here is the new one vs. the better quality Mitsu old one:
The Mitsu one is made out of real metal, whereas the knock-off ones are all plastic.
(Also, the knock-off one will not "snap" into the harness.....the little tab is a bit smaller than the OEM one.....so, I will probably have to duct tape it to help ensure it wont vibrate out.........Growwwwllllllll!)

https://cimg6.ibsrv.net/gimg/mitsubi...935e27551b.jpg

Another potential problem is that the Mitsu OEM metal one allows the "probe" to stick out further than the knock-off brand does, as seen in this pic: Thus, the knock off one will immediately be allowing more air flow to pass at idle, resulting in a higher idle speed. Unless, the computer picks up on all this data and adjusts everything to allow the engine to idle back to a normal RPM.

After installing the cheap knock-off unit, I hooked the battery back up and cranked her up. She does idle now, but its way too high....about 1200 RPM, instead of about 650 RPM where it used to idle.

https://cimg3.ibsrv.net/gimg/mitsubi...1b3d8a24ae.jpg

So, question for Hunter and the experts........Will the computer adjust its settings to allow the idle to drop back to the normal RPM? Or is this just a problem of buying a cheap part? Any other way to adjust the idle back down if the computer does not take care of the situation?

Also, if I remove these 3 screws on the Mitsu defective IAC, is it possible to clean and repair it? (at $3-400 for a new one, it may be worth a try):

https://cimg8.ibsrv.net/gimg/mitsubi...4602f6b299.jpg

Curiosity Killed tha Kat: I took apart the original OEM defective switch:


https://cimg1.ibsrv.net/gimg/mitsubi...8399749d8a.jpg


Appears to be an electromagnetic solenoid, and has small "triangles" on the inside which are connected to one of the 6 power leads. I guess 5 power leads are for various levels of current flow going to it, and one for a ground. So, looks like the solenoid should "pop" forward in 5 different increments based on how much current flow is going to it.....and the ECM or computer gives these orders. I used QTips to clean the surface area on the "triangles" and got some gray grime off, which may have been restricting the in-out motion of the solenoid. Could be that it was just "sticking" and would not open. All 6 wire leads look good, not broken off.


https://cimg2.ibsrv.net/gimg/mitsubi...529baf4f0f.jpg


https://cimg3.ibsrv.net/gimg/mitsubi...7d9602ed52.jpg


https://cimg8.ibsrv.net/gimg/mitsubi...71c8b65ef4.jpg

Small bearing on this shaft was fine. So, maybe just a good cleaning will "unstick" everything. Will put back together and give it a another try if the new "el-cheapo" one fails to allow idle to go back to the 600RPM range.
Any other suggestions?

https://cimg7.ibsrv.net/gimg/mitsubi...4a2ebfc0ba.jpg

Nice job disassembling the IAC. It is most likely a duty cycle solenoid, i.e. it turns on and off many times per second to allow just the right amount of air flow in. Not sure why you'd need 5 separate wires for that? Perhaps some are the feedback control loop to tell PCM how far the pin is moved in or out. It would be intetesting to see if internal cleaning had done any good. You are pretty much on the same track as I would be with it. You know my approach - if it's already not working and it got screws holding a cover on it - open it up and check it out. You really can't make it worse at this point. Thats the reason I have an automagic transmission from my daughter's car sitting on the bench now...
Now, back to IACs. I've never had to deal with them myself, but, I recall reading about an idle re-learn procedure on some models. I'll try to find it and post a link if I do.

Here it is:
https://mitsubishiforum.com/forum/mi...roblems-46657/

Hunter.....Thanks.....those 3 screws were on super tight, but I arm-wrestled that sucker and won. I believe that the 6 wires are needed as the computer will tell the idle to increase some when the AC is turned on, or if it goes into Drive, etc. So, I guess the computer sends power down whatever wire is needed to make the IAC pop out a bit further which allows more air to flow to the engine, and thus making the idle a bit higher.

Will clean well, and put back together and may go ahead and try it to see if the idle then goes back to the normal 650 as opposed to 1200. What bothers me is that the knock-off unit did not stick out as far (29mm vs 34mm), so it would make the idle faster just because of this fact.

Diving into your daughters tranny.......knowing you, it will be fixed and back together in a jiffy.......or, at least you will have learned alot from the effort.

That "relearning" idle procedure.....sounds like its easier just to drive the rig for a week, and let it do its own thing. However, on my Montero I was always turning the battery on/off and never had a faster idle problem after turning the battery back on. I am hoping that the engineers of the knock-off units know that the computer will re-adjust and thus the total length of the IAC shaft is not critical..........hoping. Also, perhaps mine is truly broken and something has allowed that shaft to pop out further than it is supposed to be. Skratching my head here........shoot, I could just drill a hole in the end and run a manual choke cable from it to the dash, and the problem is solved.