GVR-4 High Idle after replacing IACV

[4gfun]

I replaced the IACV recently due to 2 coils being bad. I checked the ECU for damage and I could not find bad ECU drivers.

I tried both a tan/black used IACV to no avail. I mean at this age both could be bad but I really doubt it.

The vehicle used to idle great but die when coming to a stop.

After replacing the IACV, the idle surges up and down like crazy. I can't get the idle below 2k even after adjusting the BISS and putting it in RPM adjustment mode e.g. appropriate grounding points.

No boost or vacuum leaks etc.

 

[PlanZero]

I found the easiest way to check is to keep it plugged in unbolt it and lay it on top of the throttle body. Then while standing next to the car reach in and turn the key to ON and that actuates the pintle. Turning on/off you should see that pintle move in and out. The black ones aren't guaranteed to work (actually the guy I get mine from are used but guaranteed for life, did I give you the link already?) and I've had them test OK on the multimeter and still act squirrley. Same with the ecu.
Anyway your TPS probably just needs adjustment after replacing the bad IAC. Make sure the o ring is properly seated on the IAC too. Do you still have a functioning FIAV or did you block it off/bypass plate?

 

[4gfun]

I found the easiest way to check is to keep it plugged in unbolt it and lay it on top of the throttle body. Then while standing next to the car reach in and turn the key to ON and that actuates the pintle. Turning on/off you should see that pintle move in and out. The black ones aren't guaranteed to work (actually the guy I get mine from are used but guaranteed for life, did I give you the link already?) and I've had them test OK on the multimeter and still act squirrley. Same with the ecu.
Anyway your TPS probably just needs adjustment after replacing the bad IAC. Make sure the o ring is properly seated on the IAC too. Do you still have a functioning FIAV or did you block it off/bypass plate?

You know what buddy? It was a bad ECU that I had. I had a spare fortunately. Unreal. Thanks for your time!

 

[93AWDDSM]

ECU's can do some crazy things! my car was having hellish issues a few weeks ago that turned on to be ECU related. Now I get a slight idle surge from 1100 to like 1500 once or twice and then it settles at 800 rpm. :/

 

[4gfun]

ECU's can do some crazy things! my car was having hellish issues a few weeks ago that turned on to be ECU related. Now I get a slight idle surge from 1100 to like 1500 once or twice and then it settles at 800 rpm. :/

It's getting even weirder now. Far weirder. I wonder if I have 2 bad ECUs at this point. I spoke too soon maybe.

The new ECU stops the idle surge but the idle won't go below like 1200 RPM even with the BISS screw in. In fact, when I run the jumper to put it in timing mode the idle goes to at least 2k!

It's impossible to set timing at this point. RRRRR

 

[4gfun]

I found the easiest way to check is to keep it plugged in unbolt it and lay it on top of the throttle body. Then while standing next to the car reach in and turn the key to ON and that actuates the pintle. Turning on/off you should see that pintle move in and out. The black ones aren't guaranteed to work (actually the guy I get mine from are used but guaranteed for life, did I give you the link already?) and I've had them test OK on the multimeter and still act squirrley. Same with the ecu.
Anyway your TPS probably just needs adjustment after replacing the bad IAC. Make sure the o ring is properly seated on the IAC too. Do you still have a functioning FIAV or did you block it off/bypass plate?

I don't think you mentioned a link. I guess that I'd need 2 people to check the IAC huh? That can be pretty tough around here. I am tempted to go back to my tan IAC. Too much happening at once making it difficult to troubleshoot. The TPS is at 10.1% on MMCD so good there.

 

[93AWDDSM]

I know you're post said "no Boost leaks" but are you 100% positive your not leaking anywhere in the intake tract? Insulators for injectors?

I just want to be for sure on that then, follow this. http://www.dsm.org/how-tos/tttt/tttt3.html

 

[4gfun]

I know you're post said "no Boost leaks" but are you 100% positive your not leaking anywhere in the intake tract? Insulators for injectors?

I just want to be for sure on that then, follow this. http://www.dsm.org/how-tos/tttt/tttt3.html

Yep, no boost leaks. Old injectors with good seals out down. Familiar with that guide ughhh. Lol. I guess I'll read through it again Thank you.

 

[93AWDDSM]

That should help you. He goes OCD into detail on it all haha. Mine idle varies. When it's cold it will idle at like 1300 steady until first like on operating temp. Once it's warm it will surge 2-3 times at lights, stops and then go to 800-950 and hold. Sometimes it will be 1.5k (I know for sure I have Boost leaks, waiting on gaskets hehe)

 

[4gfun]

That should help you. He goes OCD into detail on it all haha. Mine idle varies. When it's cold it will idle at like 1300 steady until first like on operating temp. Once it's warm it will surge 2-3 times at lights, stops and then go to 800-950 and hold. Sometimes it will be 1.5k (I know for sure I have Boost leaks, waiting on gaskets hehe)

Yep, I appreciate the reminder. Sometimes that's what we need. It is tough when you have a few issues going on concurrently. Just want it to be over with. I might do another BLT. The BLT is very intrusive on my vehicle so it is one of the last things that I like to do. All kinds of aftermarket stuff has to be pulled to get to it...but hey you are right. The car has been sitting for a long long time. Back then I addressed all the Boost Leaks but these cars are funny.

Just from sitting for a few years being started every few months and being driven in circles in the yard every few months the following failed:

Fuel filler hose
Injector seals all dry rotted
One brand new NGK spark plug wire went bad.
Plugs fouled
Oh and in the middle of this the brake light is now solid !

 

[93AWDDSM]

Lol, yeah it happens. I do understand some intakes require more time to disassemble to get the tester on. My buddy has IC piping that is all up in the way so it's a real headache for him. My leaks are BOV, TB shaft seal, injector insulators into head. Let us know what you find regarding your idle problems!

 

[PlanZero]

I don't think you mentioned a link. I guess that I'd need 2 people to check the IAC huh? That can be pretty tough around here. I am tempted to go back to my tan IAC. Too much happening at once making it difficult to troubleshoot. The TPS is at 10.1% on MMCD so good there.

I was describing this method for you working solo. You place the iac on top of the TB so you can see it from behind the wheel while looking through the gap in the hood at the wipers and watch the pintle move as you turn the key.
Black IACs for anyone who needs em:
https://m.ebay.com/itm/Mitsubishi-3...952746&hash=item25e290ba05:g:~ecAAOSwlQlZ5S3A

 

[4gfun]

I was describing this method for you working solo. You place the iac on top of the TB so you can see it from behind the wheel while looking through the gap in the hood at the wipers and watch the pintle move as you turn the key.
Black IACs for anyone who needs em:
https://m.ebay.com/itm/Mitsubishi-3000GT-IAC-91-99-IDLE-AIR-CONTROLLER-Control-Valve-Stealth-MD628053/162714925573?fits=Model:3000GT&epid=1224952746&hash=item25e290ba05:g:~ecAAOSwlQlZ5S3A

Got it, my eyes suck these days though. I am also afraid that I might "miss" what it is supposed to do. Let me try this and report back.

 

[4gfun]

Does the "on" position refer to the position right before I start it? If so, no movement at all. I am wondering if the drivers in the ECU are burnt out e.g. IC105 and IC107.

Doesn't have holes popped in it like they do in this link but the IC itself has a bit of discoloration on the letters and I think one of the pins *might* be burnt.

 

[4gfun]

Black IAC gives the tiniest detectable quiver known to man. Tan IAC does nothing. Internal resistance on both is correct for all coils though. All I did was put the key in the position before it starts and cycled it between that position and off a few times.

 

[4gfun]

It's the ECU and/or drivers. My spare ECU moves them just fine.

Nice!

 

[PlanZero]

Well there ya go you figured it out!

 

[4gfun]

Well there ya go you figured it out!

Yep, pain in the neck to replace the IC(s) though. Hopefully that is actually the problem. Thanks for the support.

 

[steve]

Back when I was repairing ECU's about a quarter of them had no noticeable damage to the ISC driver chips but they were still turned out to be fried when I tested them. That doesn't count the ones that I could smell being burnt up before I opened the ECU case.

 

[4gfun]

Back when I was repairing ECU's about a quarter of them had no noticeable damage to the ISC driver chips but they were still turned out to be fried when I tested them. That doesn't count the ones that I could smell being burnt up before I opened the ECU case.

I used to repair Chrysler BCM(s). That was more than 20 years ago. The smell that stuck with me was the smell of dead roaches and cigarette smoke. It's funny how those smell memories last forever.