Problem: High idle and Intake air temp error code logged (code 13)

Hoping someone can help:

Car starts and idles smoothly when cold, but when up to temp, is idling way to fast, 1500 to 2000rpm in neutral no A/C.

the idle is smooth not rough , i have cleaned ISC. cant wind idle down on throttle body, screw already at lowest setting.

check engine light is not on, but i have a fault code 13 logged at some point. (intake air temp circuit)

i will reset ECU and see if that fixes, but can someone firstly confirm the IAT sensor is part of the MAF assembly?

also does anyone have a test i can do for the IAT (ie resistance and which terminals on the MAF relate to the IAT? (Intake air Temp)

i know IAT is pin 2 on the ECU, but again not sure what the DC resistance should be.

i have openport 1.3 cable (+evoscan) on the way so i can log ECU and see what temp it thinks IAT is which may shed some light on the problem, but any advice or experience in the meantime would be appreciated.

The high idle may not even relate to the error 13, im open to any suggestions.

I initially thought a vacuum leak, but have pressure tested and cant find any.

To the best of my knowledge Eddy, the IAT sensor is part of the MAF (Evoscan even calls it MAF air temp scaled).
As you said reset the ecu, and see if it logs a fault code again, and see what AIT the ECU is seeing.

so i found loads of info on the MAF, just by Googling "Mitsubishi MAF testing".
i followed the test
for the IAT here
http://easyautodiagnostics.com/mitsubishi_maf_diagnostic/test_mitsubishi_maf_1.php
and it seemed to have no problems. I reset the ECU and the problem codes didnt return, so the IAT code was actually just a red herring.

Next i google "mitsubishi High idle" and a lot of discussion around the Idle Air Controller being a cause (Also known as, or IAC ISC or IACV. (Idle speed control, Idle air control valve)

i followed the comprehensive test instructions here:

http://www.stealth316.com/2-isc-iac.htm

and found one of the 4 coils on the ISC to be open circuit.
So i dug around looking for new IAC to match my part number of E9T15298C.(or Mitsu part number numbers are MD614978 MD628056 )
found some identical looking ones on ebay but they did not match my part number.
i emailed the ebay guy at cyberspace auto and he said he had none to match mine. wouldnt even suggest one that might work.. not much help..
the info i had read though from the US though advised they are fairly universal, so i ignored his advice & picked the one that suited the 3000GT which is part number MD614380 or 9T15271.
unit was $110 + postage
unit arrived. genuine mitsubishi factory part. 10 min install and now idling properly again
so consider those part numbers above as compatible.
hopefully this helps someone in future...

i asked the retailer at cyberspace to update his records as well....

Great work Eddy, very good info & links.

Well done Eddy, I have a high idle also and been a bit suspicious about the ISCV, so this thread helps me out a bit

No worries, just remember to clean the IAC with carby cleaner first, that can revive them for some time.

One other note, Also i am running water injection in my VR4 and thought id add about 20% methylated spirits to the reservior to create a water/metho mix. As i researched the IAC issue i did find some suspicion in the evo forums with guys running metho that the metho may eventually damage the IAC. NO conclusive evidence, just a suspicion, but ill mention it here anyway. How metho could damage something that carb cleaner doesnt is a bit of a stretch.
I did have to clean my IAC before i started on the water injection system so more likely it was already on the way out.

So this means you'll be at the cruise on friday Eddy?
I'll add your finding to the parts guide tonight as well

Great news, thanks for finding an interchangeable ISC part number. This means one day soon I can finally stop manually performing cold start high idle & heel and toe pedal maneouvres while running my aircon! Pretty sure camskill in the uk want in excess of $200 for the same part too. Nice work Eddy!

Finally got around to acquiring and fitting a new idle speed controller. As I'd wound the manual bleed screw out a few turns to keep it alive with the old controller not working, the first start after fitting the new controller had mega high cold idle, little over 2500. Wound the screw back in a few turns and it lowered accordingly. Started backing out the driveway and the idle got a little erratic, bounced between 2 and 2.5krpm. This went away with water temp gained though.

Questions: ECU reset required after fitting a new ISC? Once up to temp, does the ISC control idle at all or does it just revert to the bleed screw setting?

So it seems my idle hunt was a symptom of the brand new idle speed controller failing as I'm back to low idle and no cold start high idle routine Which begs the question: WTF is causing it to fail? Both my old and new ISC do exactly the same thing when ignition is switched on, simply vibrate a little and that's it. They should pull back to open up the passage around the throttle body apparently.

Anybody else care to check theirs for me? Does it move with ignition on or just vibrate a little?

After staring at the US and Jap 8g workshop manuals for hours yesterday trying to find some info on my ISC fault, I checked an ECU pre-requisite for the ISC to control idle. TPS has continuity across terminals 3 & 4 with the throttle against the stop which indicates the idle switch works. I guess the next step is the water temp sensor but I'm not sure about one thing: If I had a faulty water temp sensor, would the water temp gauge still work fine?

Mitsubishi sure love to use a vast array of special tools and harnesses to test things, sure would love an MUT-II. $2300 on US eBay...

Joe, have you measured the coils on both your ISC to see if they are ok? test procedure here:
http://www.dsmisc.com/dsmweb-dw/faqs.html

from memory a short vibrate at ignition on is normal i think...

and ideally you do need to reset ECU after replacing ISC.

you did reconnect the ISC connector and tighten the intake hose clamps etc after replacing ISC...?? Just checking..

You know what Eddy, that's one one of the things I've yet to test and have been making assumptions the solenoids are fine. Most of the reading I do on ISC testing states vibration at ignition on indicates continuity in the coils, no movement and they're dead. I'll crack out the multimeter again tonight and go through that test to confirm, thanks for the link

I'm usually pretty good and double check piping and connectors once I'm done That's a good point though 'cause if the ECU sees signal from crank angle sensor but gets no voltage rise from MAF it'll set the ISC to a stationary position.

The testing continues. I'll update the thread with progress of course Oh and I'll try get some pics of the test process too.

Came to the conclusion pics aren't really necessary, it's a fairly simple process.

~40Ω across all coils. So, it's fine but something else isn't. Crap. Guess I'll find and test the water temp sensor involved, then harness and possibly even go down the path of swapping the ecu if all else fails.

Admittedly it's not that hard to work around it. Undo the bleed screw a bit more and lots of left foot braking.

Did you ever find the solution to this problem?

i had idle stability problems come back agian and had much grief tracking it down, but in the end it looks to have been leaky injector o rings, (causing a vacuum leak) It was also causing my rpm to jump on deceleration, theres an extensive thread somewhere on the forum.. ive been holding my breath waiting for the problem to return, but its been quite a while now and its all good. Injector orings are fairly easy to change, about same difficultly level as spark plugs.

Describe your idle fault Danners. What happens and when?

My issue is kind of the opposite of the one this thread is dedicated to. My problem is when I initially start the car it will cough and splutter for 3 or 4 seconds, or sometimes stall. After the spluttering is finished, idle returns to normal. If I decide to drive the car immediately for the first few minutes it is very sluggish and hesitant to accelerate. Once warm, the car seems to be fine. If I have driven the car for 10 minutes or so, turn it off and start it again there will be no issue, however if i leave it for a few hours (say 4 or 5) the problem will be back again. The longer I leave it, the worse it is usually

I have tried:

1. Replacing fuel pump with a Walbro and changed the o-ring
2. Reloading a stock ROM on the ECU
3. Replaced as many vacuum lines as I can see with new silicon ones
4. Tightened as many clamps as I can see
5. Replaced injector o-rings
6. Installed a new battery
7. Changed from a POD filter to an ARC air box, with a brand new filter
8. Installed after-market coilpacks from the group buy run on the forum
9. Removed the ISC and checked it's function by turning the key on and off (I have not performed the OHM's check yet)
10. Checked TPS is set at 13.3% based on Steve's advice
11. Installed the fuel rail loop from the forum group buy

As you can see i'm running out of things to replace/try! I think i've either missed a vacuum leak somewhere, or my ISC isn't working properly... even though it moves in and out when the key is turned. I'm certainly up for any suggestions!

I might start a seperate thread so more people might read this

Vacuum leak somewhere is my guess....

Test your ISC! At least then you can rule it out.