Hptuner failure & IAC
Thread Starter
On The Tree
Joined: Aug 2013
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Hptuner failure & IAC 
Unit used less than 10 times.
Long story short I have an mpvi2 that is on way back to hptuners. Fairly certain unit is defective. However here is what happened. The unit was having issues connecting. I figured it was my side of things so I uninstalled and re installed software.
I reflashed car after making some adjustments to throttle cracker and as it was writing and doing its thing I washed the car. I open the door and it was done. I start the car and immediate very high idle. Like entire brake booster hose was off. 3000rpm. I was like oh man. I pulled car into garage and thought maybe this unit is going bad. I tried to do a reflash but unchecked the high speed write. It started to erase and failed mid erase and car wouldn’t start. After about a dozen controller unlocker errors I wound up disconnecting the battery and opening vcm editor from original folder and it finally reflashed. The high idle is stuck there and I start trouble shooting this. Iac valve is fully retracted and it will do nothing but vibrate when I command different counts in the scanner. Even a new ac delco will do nothing. If I manually pull out iac valve and disconnect and reinstall the car idles pretty close to set rpm. I’m almost certain it’s not a mechanical issue but a software/electronic fault. I hooked up the mpvi2 to laptop today and it won’t even recognize. In the mean time has anyone had this happen? Should I go ripping into the iac harness or do you think a clean write with a good tuner will fix this? This is incredibly frustrating and stressful so I guess I’m just fishing for someone else’s experiences. Also considered bad pcm or iac drivers? Connectors on pcm harness are red/blue.
Teching In
Joined: Jul 2018
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I got this from the sloppy site:
IAC Relearn Procedure
If you are having idle issue you may need to reset your Idle Air Control (IAC) and
TPS, do this before you start drilling holes in your throttle body (TB) blade. I have
used this procedure on some huge cammed cars and it worked.
1) Monitor your IAC, Idle Speed, throttle position voltage and your throttle position %.
2) With the key in the ON position, adjust your TB set screw until your throttle position
is 2%.
3) Turn your key to the OFF position.
4) Unplug your Throttle Position Sensor (TPS) and IAC.
5) Turn your key to the ON position for a few seconds, and then OFF again.
6) Plug in the TPS and IAC and then turn your key to the ON position and restart
logging. Your throttle position will now be reset to 0 degrees and about .45-.55 volts.
7) Start your engine, your IAC should be 40-60 for a cammed engine.
if you are not at your desired IAC position redo the above procedures in smaller
increments.
Thread Starter
On The Tree
Joined: Aug 2013
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After failed googling does anyone know which sensors the pcm uses to control the iac valve? I’ve lost my multimeter so not sure on wire continuity yet but at this point I’ve determined with iac unplugged and extended out to a certain spot car runs 100% normal. I’m just trying to button up any stupid little thing it could be before I get my hptuners back. Also to check the iac harness can I just test continuity between the two circuit drivers at the harness or do I have to pull pcm pinouts??
Teching In
Joined: Jul 2018
Posts: 29
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Do you try re setting your iac? Imo it is working fine. The computer is telling it to do something and its doing it. The thing is the computer will tell the iac move x amount of steps and it will move. The problem is were is it moving from. That is why you need to reset it or home it. That way the iac. For example the comp commands 25 steps, the computer is assuming te sensor is at 0 steps and has no way to verify this. So if the sensor is sitting anywere other then 0 it will still move 25 steps, but will end up in a different position and give you drama.
I think when your write failed, your iac home was set incorrectly for whatever reason.
I think when your write failed, your iac home was set incorrectly for whatever reason.
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Thread Starter
On The Tree
Joined: Aug 2013
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It seems like it isn’t extending or closing airflow and only opening it. Also I don’t think ls motors have a procedure for initial iac set or install??. From what I thought a key on/off cycle would reset it. But I’ve unplugged tps and iac and did the tps reset as well. If I were to command steps from 0-128 in hptuners the pintle showed no visible movement. Motor would vibrate. That was about it. I’m not sure where to go from this point besides checking the wiring. Car has new IAT,TPS,and now IAC. Also when I would plug in iac after I had it running smooth. Pcm would command iac to fully retract eventually I’d be idling about 3,000
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On The Tree
Joined: Aug 2013
Posts: 139
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Iac harness to pcm connector showed continuity for each lead. I have no idea what else it could be besides the write error and failed hptuners. Or IAC drivers in pcm...here’s to ripping my hair out. Shoulda went EFI Live 
Thread Starter
On The Tree
Joined: Aug 2013
Posts: 139
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Yea that’s what I’m hoping for. I was just trying to button up everything I could on my part. It had a slightly high/ slow idle drop due to throttle cracker table needing a small reduction across the table. But I don’t think it’s anything mechanical at this point.
Thread Starter
On The Tree
Joined: Aug 2013
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For an update on this I wound up replacing the pcm and idle is back in control. I had an issue keeping a scanner linked up and scanning as well, would keep losing connections, that is now gone as well. However other issues have arose. My speedometer is now not working. Also just before new pcm went in I threw a maf po102 code and car ran like garbage unless deep in the throttle. Replaced maf and pcm at same time. Iac is controllable now and idle is now Good. Car still runs bad though. At WOT car runs fine. O2 sensors are pretty new. LTFT are disabled and I run off short terms and noticed that they are way up there sometimes reading 18-20s. All being said the car almost shuts off when it does this. I’m kind of hoping fuel filter is bad as pump is newish as well. Less than 10k. Anyone know what to do about this speedo? If I pull the dash fuse for gauges and reinstall it I can see it lift off the needle stop.
Check your Speedo calibration. Dealing with another bricked ECU, replaced it, wrote tune, speedo off by 1000x. Should be 29k but was 29. Not saying yours is low. Might be crazy high
Did your write entire take?
It *seems* like the new MVPI2 is writing back data into the wrong places. Different OS's vary in length and store data in different places in the binary code itself.
It *seems* like the new MVPI2 is writing back data into the wrong places. Different OS's vary in length and store data in different places in the binary code itself.
Thread Starter
On The Tree
Joined: Aug 2013
Posts: 139
Likes: 3
It erased and fully wrote, did it’s clean up and said was complete. I have a log I can post I took yesterday if you want to check it out. Ive yet to hook a fuel pressure gauge up to the rail to figure out the part throttle issue. I don’t know if you can see the driveability issue but At cold start it didn’t want to idle or respond to throttle input very well. Just had to keep it running for it to warm up. After that I guess it went through it’s relearn and idled good. Just at part throttle and say revving to take off the engine acts like the traction control kicks on and rips power out. It’s very odd. But I will try and get to the fuel filter sometime today and change that. I’ll make a some kind of change into the speedo tab then write calibration and redo the gear tire wizard and rewrite calibration only and see if that works
Last edited by Lt1slowerbird; Sep 1, 2018 at 02:29 PM.
Thinking i should buy every mpv1 i see just to have a backup lol or atleast until they figure out what's wrong with their mpv2
Thread Starter
On The Tree
Joined: Aug 2013
Posts: 139
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Yea it opened up a huge can of worms for me. The speedo ran fine until the new computer. However I did pull the intake off and everything to put new intake gaskets in. Even though they were already new I figured that’s what it was causing an idle that high with no vac leaks but then afterwards I come across a thread speaking of iac drivers and sure enough that was the cause. I figured my iac was operating and everything since I had continuity to the pcm but of course that wasn’t the case. So either the new computer is not jiving with my speedo(idk if that’s even possible) or I discovered a bad signal wire by pulling the intake and tugging on the harness maybe. pcm is seeing speed but cruise odometer and speedo not working. It’s very frustrating to say the least. I’m highly upset by this whole experience and my electrical skills are VERY limited when it comes to circuits and things like engine harnesses so I’m going to have a hard time diagnosing if a bad wire or not as I only have a multimeter. First thing is I’ll throw the old computer back on and run with iac manually set and unplugged and see if speedo works again. After all of this headache I don’t think cheaping out over EFI Live was worth it. But as of right now does anyone know how to test the circuit that sends speedo signal? If I’m right if computer is seeing speed is has nothing to do with the vss sensor or wiring right? Just the straight signal wire? And if that’s the case the only test I can do is a continuity test from pin 50(I think) to the gauge cluster right?
Thread Starter
On The Tree
Joined: Aug 2013
Posts: 139
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Just an update Before I dug into chasing wires I swapped my old pcm in and left it sit up on the passenger fender well and took a little ride down my driveway and what do you know the speedometer worked. Idle went apesh*t but atleast I know everything is fine with it’s wiring. Does anyone know of any way to recover my original pcm that’s been scrambled like this as apparently I just can’t win. Got a this reman pcm from eBay programmed for my vin and everything and paid for a license, just about my luck lately with this car..... 
Just an update Before I dug into chasing wires I swapped my old pcm in and left it sit up on the passenger fender well and took a little ride down my driveway and what do you know the speedometer worked. Idle went apesh*t but atleast I know everything is fine with it’s wiring. Does anyone know of any way to recover my original pcm that’s been scrambled like this as apparently I just can’t win. Got a this reman pcm from eBay programmed for my vin and everything and paid for a license, just about my luck lately with this car.....