Hello Everyone,

I apologize that my first post has to be about an issue, but I'm at wits end! I recently purchased a 96 Montero SR OBDII and shortly thereafter I discovered a strange (to me) problem.

So what happens is that at some point in driving the car it will begin to idle between 1.5 to 2K. The idle might be at 2K and drop slowly to 1.5K, then jump to 2K and repeat. It doesn't matter if the car is in gear or parked. HOWEVER, if I turn on the AC, it idles perfectly near 800K.

But what I noticed on Saturday was that for part of the day the idle was fine. But when the idle was ok, sometimes the car would crank but not start (after driving and parking for anywhere from 15 min to 1 hour). BUT, if I turn on the AC prior to starting the car, it would start fine!

On a side note (not sure if this is normal, and if not, related), If I'm driving at 45 or 50MPH, and lift off the throttle in 4th gear (its an auto), I see the revs fall from 2k to maybe 1,250, then then go back up to 2K and repeat. Not sure if it is normal or not.

So my research lead me to possibly a bad IAC. I bought a used one from eBay. The unit in my car is the beige unit and the eBay unit was the black one (newer unit, slightly smaller). After installing it, I noticed no difference. If anything it seemed worse. So I took it off.

Now I have no idea what is going on. Any help would be greatly appreciated.

BTW: No check-engine light at anytime during these issues.

It will take some digging to get at, but you need to check the intake runner changeover butterfly shaft in the lower part of the intake. The shaft bushings wear too easy, and leak a lot of air, making for a very high idle. Also check for vacuum leaks elsewhere in the vac lines (I use a piece of vac hose to the ear and trace the other end over the lines, listening for a whistling sound of the leak leakin'.

The black ISC is a superior part to the old beige one. Reinstall it, after you test out the coils per the fsm.

90% sure it's an intake leak of some kind...

Thanks so much fasteddy! With respect to this butterfly valve, is this in a spot on the intake tract between the throttle body and air filter or in a different spot? What section of the service manual do I find info about this?

Look in the 92-96fsm, in the 3.5 engine section, or in the mpi system, can't remember which right now. Steps to get at it are in several posts on here. Might as well get used to our cranky search function. Some search tips. It will search a 7 year range max, so set the search for from 7 years ago to today. Input the terms "butterfly shaft", and only select the mitsubishi tech section to search. It'll be in there, with a lot of extraneous stuff. Oh, yeah, search title and body of posts SECOND, only if a search of titles doesn't find your "lookin' for" in the titles.

It's way down in there, almost down to the top of the vee of the cylinder heads themselves. In short, you disconnect (and LABEL as you go, with pics, lots of pics, trust me...) all the little hoses and wire connectors and throttle cables and air hoses and probably the fuel lines (careful-a little fuel will squirt, catch rags needed), then remove the upper intake manifold, with the throttle body and plenum and intake runners (you'll see the two sets of intake runners, one set long and skinny for good flow velocity in the smaller tubes, and long length for good intake resonance ram effect all to boost low end torque, and a second, fatter, much shorter set of runners to feed the motor at above 3000rpms, fat for much higher air flow, and short for good ram effect and higher rpms.

Below this big old hunk of aluminum (which was bolted on with a couple of rows of long bolts - note and draw a diagram and sharpie #'s on the bolt heads so you put them back in the right place! - running down the centerline of the motor), there's the lower intake, bolted the the heads on each side, with a row of alternating size holes down the middle, the small ones mating to the low speed upper intake runners, and the large one mating the hi speed runners. Where these meet in the center of the lower intake, lives the possible gremlin, the intake runner changeover butterfly valves and shaft and what I strongly suspect are badly leaking shaft bushings, plastic doughnuts that are leaking air (high idle, lean mixtures, hard cold starting, bad emissions) and letting the butterflies flutter in the rushing intake air. This is MOST dangerous in the long run. The fluttering of the butterflies fatigues the tiny brass screws holding the b'flies to the shaft, and the round butterflies dive off into the cylinders and pistons and valves and combustion chambers and the flying pieces thereof soon engendered. Dead motor. $$$$$$$$$. You can cure it with a new lower intake with improved bushings, 400ish bucks, or bandaid it by unplugging the actuator hose and wiring the shaft arm in the location of your choice (normal rest postion is on the low speed runners, probably a good choice, I'd go halfway between as an experiment...) and sealing the outside air ends of the shaft with rtv goo

This is a doable if necessary task, so you check everything else in sight first. If your ecu is obd2, you can buy a cheap code reader and scan the codes and report back, and we can start sending you in the right checkin' directions.

'Twer me, I'd download the factory manual pdf from montymcv's site (I think the link is the the fag's) and read the stuff on the drivability troubleshooting probably in the fuel section, with error code lists and diagnostic trees that send you in reasoned out directions based on your described symptoms. Maybe you can do all the tests with home stuff, maybe not, but with the e codes and the book, we can logic most of it out from what you can dig up.

In my 91 3.0, which is of course totally different animal so take it for what it's worth and take fasteddy's advice first...my RPMS used flop up and down when coasting with foot off the gas. Almost like a switch was going on an off cycling it between 1000 - 2500 rpm. Also idled erratically. After replacing the IAC with no change, it turned out to be a fried ECM for me. Just throwing that out there.

Thanks again gentlemen. It is a bit of a conundrum. It could be the ECU, for which I can spend $110 used from eBay to find out. But it could also be the butterflies. But to find out, I really need to have a mechanic open it up to see. If that is not it, then obviously I gotta pay labor, if it is I gotta pay labor AND replacement parts! Fantastic!!! I did find the tech article here for the 95, but honestly I don't have time nor the space for that level of work.

I think no matter which "road" I take it will be a bit costly. But the alternative is to have the entire engine go bad. For the record, I know OBD2 cars are sensitive and will throw codes if they sense something is wrong. With mine, no CE light and no codes. I checked with my generic scanner. And my mechanic has looked with his scanner.

Mike, do you know anyone in LA who has a 96 SR (94-96 SR's are all different unfortunately especially the 96 when they went to OBD2 compliant ECU's) that you could swap your ECU with?

If necessary double-check that your vin and theirs will use the same ECU using the mitsu ASA app.

Unfortunately I don't. But I will keep an eye out. Thanks again!

If you were closer to me up here (Tracy/Manteca area) I'd be happy to swap them to help you determine if it's actually the ECU or something else entirely.