IAC Question

[Atrais]

So my Monty's had sort of a rough idle ever since I got it. It's VERY slight, sometimes unnoticeable, almost feels like a misfire even though I know it's not. I checked the resistance on it yesterday and got 44 ohms on all the pins which puts it out outside the normal range according to the FSM. So I'm looking at snagging a parts store (O'Reilly's) replacement as Mitsu wants close to $400 for a new one and the only other option (a website selling new IAC's called DSMIAC) is apparently now defunct as they can't accept Paypal and won't answer emails. Anybody running an aftermarket IAC with any luck? I'm trying to decide on this or hunting through a junkyard for one.

Btw: I know it's not a vacuum/spark/fuel issue. I just did the full timing belt, plugs, all the filters, etc about 2k ago. It runs great just has a very slight stumble at idle sometimes. I'm getting ready for an 18hr trip this month so I'm going through the truck again before heading out.

 

[BEG]

RTM Racing has a genuine Mitsu ISC for about $209 USD (They're in Canada):
https://www.rtmracing.com/xcart/product.php?productid=19168&cat=1918&page=1

Otherwise, they have an aftermarket version as well for about $95:
https://www.rtmracing.com/xcart/product.php?productid=19168&cat=1918&page=1

I've been very satisfied with them in the past and they're more than happy to answer any application questions even if it's not for DSM/EVO cars. If you don't mind taking a chance on a cheapie, Amazon has one for about $22:
http://www.amazon.com/Control-Mitsubishi-Diamante-Montero-MD628059/dp/B01176MLC0

 

[jeep-N-montero]

RTM Racing has a genuine Mitsu ISC for about $209 USD (They're in Canada):
https://www.rtmracing.com/xcart/product.php?productid=19168&cat=1918&page=1

Otherwise, they have an aftermarket version as well for about $95:
https://www.rtmracing.com/xcart/product.php?productid=19168&cat=1918&page=1

I've been very satisfied with them in the past and they're more than happy to answer any application questions even if it's not for DSM/EVO cars. If you don't mind taking a chance on a cheapie, Amazon has one for about $22:
http://www.amazon.com/Control-Mitsubishi-Diamante-Montero-MD628059/dp/B01176MLC0

I am almost willing to bet money that the aftermarket unit sold by rtm and amazon are the same identical part.

 

[BEG]

I am almost willing to bet money that the aftermarket unit sold by rtm and amazon are the same identical part.

You're probably right, but since Rock Auto lists aftermarket ISCs in the $85-and-up range I figured the $22 part was probably not up to snuff. Still, I'd order the one from Amazon first knowing I'd only be out a few bucks if it didn't work.

 

[Atrais]

Thanks for the links! I didn't know about RTM at all. The local parts store down the road apparently has a BWD (Borg Warner) version of the part in stock so I'm going to hop down there today with the multi-meter and see what the resistance looks like on it. If it's good I may snag that, if not I'll give the RTM unit a go I guess. BEG, are you running one of their IAC's?

 

[BEG]

Thanks for the links! I didn't know about RTM at all. The local parts store down the road apparently has a BWD (Borg Warner) version of the part in stock so I'm going to hop down there today with the multi-meter and see what the resistance looks like on it. If it's good I may snag that, if not I'll give the RTM unit a go I guess. BEG, are you running one of their IAC's?

No, but I've used a lot of their plumbing/fuel line upgrade parts and expertise in the past. I've also had good results from www.3sx.com for DSM/Mitsu parts. Here's their aftermarket offering:
http://www.3sx.com/store/comersus_viewItemBundle.asp?idProduct=30504

 

[jeep-N-montero]

The main issue I have ran into is that a lot of Chinese-built aftermarket sensors are not within the same tolerances as OEM, to the point that the OHM measurements can be all over the place even between 2 identical sensors from the same maker. On the upside BWD is one of the better brands you can buy if not going OEM.

 

[jeep-N-montero]

Here is some info on the BWD part http://eaccess.smpcorp.com/ecatalogs/std/CatalogSearch.aspx?p1=classic&vehicle=248661&Part=AC249

 

[jeep-N-montero]

$129 on Amazon http://www.amazon.com/Standard-Motor-Products-AC249-Control/dp/B000C7WQYY

 

[Toasty]

I bought an aftermarket one from Rockauto and it lasted 6 months. Same with their TPS plus it wouldn't get all the way in to spec from the beginning. Go OEM and forget about it for a long long time.

 

[Salonika]

I had an idle issue that sounds almost exactly like what you are describing. I removed and cleaned the throttle body and installed a new IAC motor. No change. I brought truck to dealer to have them perform a recalibration procedure that the FSM describes. $75 in labor later, nice smooth idle.

 

[Atrais]

I bought an aftermarket one from Rockauto and it lasted 6 months. Same with their TPS plus it wouldn't get all the way in to spec from the beginning. Go OEM and forget about it for a long long time.

Honestly this is my go to solution for most OEM electronics. But in this case the cost of the unit paired with the timeframe I'm working in makes sourcing an aftermarket unit a reasonable alternative.

I had an idle issue that sounds almost exactly like what you are describing. I removed and cleaned the throttle body and installed a new IAC motor. No change. I brought truck to dealer to have them perform a recalibration procedure that the FSM describes. $75 in labor later, nice smooth idle.

Interesting. By recalibration procedure are you talking about messing with the throttle body screw by setting the truck at base idle? I have a scan tool that I'm PRETTY sure I can lock the truck into base idle with. I may try that if cleaning/the new unit don't work.

Can you describe your condition? I'm wondering how similar it is to mine.

 

[Atrais]

BTW I picked up the BW unit today and took some ohm readings. All the coils measured at 40 ohms +/- .5 which from what I've read is where the "new" black plastic IAC's are supposed to be. What's interesting is the one my truck currently is only 4 ohms out making me think that a good cleaning may bring it back down into service limits...

 

[Painted Mountain]

maybe IAC maybe something else

Just my two cents.

I bought a 99 montero that had been sitting a while. It had a similar issue. idle bounce. Once the vehicle warmed up though the bounce pretty much cleared up entirely. From a cold start the idle would go to around 1200rpm and slowly drop as it warmed up as it should... but once it got down to about 900rpm or so this idle bounce would start.

I checked so many sensors one by one. Of course the IAC was early on that list. I got on the phone with an engineer in Texas who rebuilds IAC motors and computers for these Mitsubishi's and a few other manufacturers. His technique for testing the resistance of the IAC was to test from the center pin to the left and center pin to the right on each row. Then compare that number to the resistance on the outer two pins of each row (skipping the center pin). The outer pins resistance should be roughly double. These can also fail mechanically but apparently this is much less common.

I tried a new IAC anyway just to be sure and it didn't help at all.

In my case it ended up being a MAF sensor. I tried to go cheap and get one off ebay but it too was off (cleaning didn't help). Ended up with a rebuilt one and it works perfect.

Check your fuel trims to see if a clear pattern presents itself. My old MAF was stuck reading lean causing extra fuel to be added and thus an ugly bounce. Fuel trims got a little better under load. Points to a vacuum leak but I ruled that out.

Maybe this helps or maybe just incoherent gibberish.

Either way best of luck!!

 

[JohnnyBfromPeoria]

Sounds like Painted Mountain may be on to something. I doubt the IAC would be that "off" at the readings of 44 ohms, particularly if the outside pins are roughly double what the inside-to-outside pin readings are. Mine was about 44 ohms as well. I cleaned (carefully) the passages in my throttle body and reinstalled my old IAC and left it alone (95 SR with the 3.5 DOHC). I too would be looking more at the MAF since it has so much control over most aspects of fueling when the vehicle warms up.

John B.