Evo 8 Won't Idle
 

Hey Guys,

I took my evo out on Sunday and it drove just fine, the car has a history of being a lemon due to previous owner complications BUT its been good to me for about 3k miles now after engine replacement (used evo 8 block with 40k miles, the head was rebuilt and has new valves/guides, everything has been replaced with OEM parts including belts/tensioner/fluids/gaskets/bolts). I decided to take the car to work yesterday and it started and died instantly, so I tried to start it again but it died instantly. If I feather the throttle it will stay running, but when I let off, it dies. If I continue to hold the throttle down until it warms up, it will idle on its own but it jumps around and tends to stay on the lower RPM side appearing to almost misfire.

Engine is mostly stock (and I actually mean that) All it has is evo 9 turbo, evo 9 recirc, AMS exhaust, walbro 255 and solid motor mounts (mounts cause the car to vibrate pretty good, maybe something came loose that I cant find?)

No codes present
Timing is spot on
No vacuum leaks
Double checked spark plug gap - plugs are good
FPR doesn't have fuel coming out of vacuum line
Fuel pump primes
Has a quarter tank of fuel - fuel is not old
Oil/Coolant is good/clean/full
Compression is good
Battery/Grounds are good (tested with multi-meter)
All engine sensors and ECU are plugged in, nothing is loose or broken

So now, I am at a loss of what I should do next since the car won't give me any sort of data of where I need to be looking for diagnostics and all basic diagnostics check out.

How about your coils? Check that wiring set up and then maybe test each coil for spark.

I had the same problem on the same car. I searched through many posts such as this as well as posting my own. Some people said bad IAC. Some people said bad EGR valve. Some people said it was the tune and so on. The problem on mine happened to be a bad serpentein tensioner pully. Minght be called the alternator pully. It wasn't keeping the belt tight enough at idle to keep the alternator going. No noise coming from the area to lead me to that it was just bad. It minght be that. Of If u do need a new one pay the extra for the OEM. I bought the Napa special and regreated it cause it was slightly larger than OEM and a pain to install. Hope that helps

Thank you for the tips! I have an update that may help direct the issue to electrical:

I cleaned the MAF sensor and cleaned/tested the IACV yesterday, while I did that I unplugged the battery.
After reinstalling both sensors the car started up just fine and it idled exactly where it needed to be, no hesitation.

I drove the car around town, went to put fresh fuel in it and then when I turned it off at the gas station to fill up it died again after trying to restart it and wouldn't idle. I kept my 10mm with me and took the negative cable off the battery again for a few seconds - tightened the terminal clamp and car fired right up just fine as if nothing happened.

I drove the car home, got to my driveway and turned it off. attempted to restart it, would start and die just like the initial issue. I disconnected the battery again, reconnected it, car started just fine. Turned it off, attempted to restart, would start and instantly die again.

Wonder what disconnecting and connecting the battery would have to do with it not idling?

Edited reply - would also like to add that I did replace the idler pulley a few months back due to bearing failure, the serpentine belt appears to have good tension yet.

Have you tried scanning it for codes? Try to start it a few times and after it dies, scan it. Sometimes codes will be pending and not show a check engine light. Sounds like disconnecting the battery is "resetting" something temporarily.
Also, how's the condition of your battery cables? Clean any corrosion off if there is any. Make sure the ground/s are all tight.
Another idea would be to test to make sure the MAF is indeed good and not on its way out.

Yes, I have scanned for codes before I disconnected the battery previously. No pending codes, no active codes unfortunately. I whish the car would be more precise on where the issue was, its like a child that says they are sick but won't tell you if they have a headache, sore throat or stomach ache. HAHA

The battery did have some corrosion but tested just fine, I did clean the corrosion off along with checking all the grounds and cleaning off dust/dirt/corrosion and ensuring they are tight.

MAF has 12v on the power circuit and a 5v reference with KOEO

I will try getting the car to set some sort of code tonight, hopefully after a few cycles it give me something to work with.

Does it have an OEM IACV or one of the cheaper replacements?

It has the OEM IACV - when I removed the valve and tested it, it moved freely when I had a friend cycle my key.

ok cool. Have you tried setting the BISS with evoscan?

Nope, I have not done that yet. Good call. I will attempt to tonight or tomorrow and report back.

Well, the idle adjustment didn't change anything. Car idles where it needs to be after I hold throttle down for a while... I'm at a loss.

Only other thing I can think to advise without seeing a log or being there is to do a boost leak test and pay extra attention to the throttle body and intake. Soapy water will show leaks with bubbles. I know you said you have no vacuum leaks, but a boost leak test really is the ultimate way to track down leaks. Assuming you haven't already done one. At this point though without seeing some logs of the problem I would really just be throwing guesses out there.

U can check the alternator easily as well to rule that out. Simply start the car and then remove the negative from the battery. If the car dies or starts to stall u have a bad alternator. Just hope it's not that cause alternators on evos are in a horribly inconvienent spot.

Try pulling fuel pump relay 3. It's possible your fuel pressure is too high to start and flooding your cylinders.