IW STi Forum banner

1 - 19 of 19 Posts

·
Registered
Joined
·
554 Posts
Discussion Starter #1
Hey guys.

I did a quick search but didnt really find anything that was similar to my situation. Basically on a cold start, the car starts up normal but after 10 sec or so it starts hunting around rpms like in this video. Once it warms up, the crazy idle stops.

Not my video. EDIT:i cant get the video to embed: STI 2007 cold start problem - YouTube

On top of that, i've been having pretty horrible throttle response. When im idle, and i give it a little gas, it will stumble for a second and then rev up and same when i downshifting and blip the gas.

72k on the car and it hasn't been driven much at all in the last 6 months maybe about 2k miles? could it be a dirty MAF? I know the drive by wires dont have a iacv...
 

·
Registered
Joined
·
139 Posts
Check the TGVs, MAF, possible vaccuum leak.

Modlist will help? what tune are you running?

The more information you give, the better answers you will get.
 

·
Registered
Joined
·
554 Posts
Discussion Starter #4
Fuel & Tuning:
Cobb AccessPort v2
93 Unleaded
850cc DW injectors
NGK one step colder spark plugs
Walbro 255l fuel pump
Grimmspeed ECBS
Efi Protune
Engine
Gates Racing Belts (AC/Alt)
Motul 5w30

Exhaust / Intake:
Invidia N1 Catback Exhaust
Invidia V2 Catless Downpipe
Stock Airbox w/ K&N filter and silencer delete
Grimmspeed Uppipe with EWG Kit and Dumptube
Tial 38mm External Wastegate
Perrin Turbo Blanket
DEI Gold tape on intercooler

it gets worse the colder it is outside in the morning. Vacuum leak would be still be present when it warmed up unless it was a very very small leak. what to check on the TGVs = the motors?
 

·
Registered
Joined
·
2,869 Posts
It might have something to do with the maf sensor because the car is reading off of the maf sensor only, on cold start ups. Then the o2 sensor kicks in once it gets up to temperature which could be the reason that the problem goes away. Try cleaning or even replacing your maf sensor. Or if you know some other subie owners, ask them to loan you theirs for second.

I had the same thing happen to my car but opposite. It happened when it got warm(when the o2 sensor kicked in) and didn't happen when it was cold because it was only running off the maf.
 

·
Registered
Joined
·
554 Posts
Discussion Starter #7
It might have something to do with the maf sensor because the car is reading off of the maf sensor only, on cold start ups. Then the o2 sensor kicks in once it gets up to temperature which could be the reason that the problem goes away. Try cleaning or even replacing your maf sensor. Or if you know some other subie owners, ask them to loan you theirs for second.

I had the same thing happen to my car but opposite. It happened when it got warm(when the o2 sensor kicked in) and didn't happen when it was cold because it was only running off the maf.
that seems like a good idea. i'll pick up some maf cleaner this weekend and give it a quick shoot. taking out the maf is a lot easier than ripping the coilpacks and plugs to do a compression test.:tup:

you know what, know that i'm thinking about it, if i blip the gas while its doing its rpm dance, it will stop right away...
 

·
Registered
Joined
·
2,869 Posts
that seems like a good idea. i'll pick up some maf cleaner this weekend and give it a quick shoot. taking out the maf is a lot easier than ripping the coilpacks and plugs to do a compression test.:tup:

you know what, know that i'm thinking about it, if i blip the gas while its doing its rpm dance, it will stop right away...
Try unplugging your maf and then starting the car, when its cold. See if it runs any better, you will get a CEL but if it runs better then it is the maf. Or unplug it while its running, might cut the car off though.
 

·
Registered
Joined
·
554 Posts
Discussion Starter #9
Try unplugging your maf and then starting the car, when its cold. See if it runs any better, you will get a CEL but if it runs better then it is the maf. Or unplug it while its running, might cut the car off though.
This is it. i started it this morning (about 40 degrees F) and it was starting to rev up. i pulled the maf harness and it immediately leveled out.

NOW i have a CEL and the cruise is flashing. after i clean the maf should i pull the battery term to do a reset to get rid of the cel?
 

·
Registered
Joined
·
615 Posts
This is it. i started it this morning (about 40 degrees F) and it was starting to rev up. i pulled the maf harness and it immediately leveled out.

NOW i have a CEL and the cruise is flashing. after i clean the maf should i pull the battery term to do a reset to get rid of the cel?
plug in you ap with the key in the on position, go to the troubleshooting menu, reset the ecu from there. That will clear your code.
 

·
Registered
Joined
·
2,869 Posts
Cool man, I have a simple code reader that my brother bought awhile ago and thats what I use to view and delete codes.

If cleaning it doesn't work then it must simply be bad, but hopefully cleaning it will do the job.
 

·
Registered
Joined
·
1,319 Posts
I hadn't noticed before that you have a drop-in K&N. The oil from those filters have been known to foul the MAF's from time to time especially if they are over-oiled when serviced.
 

·
Registered
Joined
·
554 Posts
Discussion Starter #13
plug in you ap with the key in the on position, go to the troubleshooting menu, reset the ecu from there. That will clear your code.
I'll clean it tonight and reset it. TY for the input

Cool man, I have a simple code reader that my brother bought awhile ago and thats what I use to view and delete codes.

If cleaning it doesn't work then it must simply be bad, but hopefully cleaning it will do the job.
Yeah i'm hoping it just needs to be cleaned.

I hadn't noticed before that you have a drop-in K&N. The oil from those filters have been known to foul the MAF's from time to time especially if they are over-oiled when serviced.
Yes i thought about that...there's not much to do about that other than going back to a stock filter.:tdown:
 

·
Registered
Joined
·
13,088 Posts
I also use the K&N, though others here howl about them ruining engines. :notsure: works fine on mine.

I'd take it out, clean it up, dry it out, and lightly oil it. DO NOT SATURATE!

I pull my filter on saturday morning, and let it air dry. Typically by Sunday morning/early afternoon its ready to be oiled.
 

·
Registered
Joined
·
1,319 Posts
Yes i thought about that...there's not much to do about that other than going back to a stock filter.:tdown:
Yea I hear ya. I think there are some performance dry options though. I know HKS, Blitz, Apexi, Cosworth, and Prova all make dry drop-ins and I'm sure there's more.

Otherwise yea just go really light with the oil. I always had trouble with over oiling because with the oil always seemed to come out of the can in a stream. I bought the Cobb intake and that too has a wet filter. When the time comes for service if I can't get the oil on there lightly enough I'll try to fit an AEM dryflow filter. We'll see.
 

·
Registered
Joined
·
1,174 Posts
My LGT does something similar but the revs go up and down more slowly and the range isn't quite as much. AFR also goes up and down as the same time, +/- 0.5 or so. Not enough to stumble, but enough to affect the RPM.

My guess (unconfirmed) is that it's caused by the ECU trying to heat up the catalytic converter by leaning out the AFR periodically. If it's just adding and subtracting a fixed value from the injector pulse time (like it does for cranking and startup), then going to bigger injectors would cause the AFR change to be higher than they really wanted. I have been meaning to investigate this further but haven't gotten to it yet.

Will the AP let you log any if these?

Final Fueling Base
Closed Loop Target AFR
AF Correction #3

If so, try logging those, along with:

RPM
MAF (g/s)
Load (g/rev)
Accelerator pedal angle
Throttle opening angle
AF Sensor #1
AF Correction #1

My guess is that the first 3 will show the target AFR bouncing around, and the TOA parameter will show the idle control playing catch-up.
 

·
Registered
Joined
·
1,174 Posts
Also, if you stab the throttle while it's doing that, or if you try to drive, does it immediately go back to normal?

Mine does, which is part of the reason I think it's just an emissions thing. Idling with a cold cat is just about the most toxic thing your car can do. Other than WOT pulls with no cat, of course. :)
 

·
Registered
Joined
·
554 Posts
Discussion Starter #18
My LGT does something similar but the revs go up and down more slowly and the range isn't quite as much. AFR also goes up and down as the same time, +/- 0.5 or so. Not enough to stumble, but enough to affect the RPM.

My guess (unconfirmed) is that it's caused by the ECU trying to heat up the catalytic converter by leaning out the AFR periodically. If it's just adding and subtracting a fixed value from the injector pulse time (like it does for cranking and startup), then going to bigger injectors would cause the AFR change to be higher than they really wanted. I have been meaning to investigate this further but haven't gotten to it yet.

Will the AP let you log any if these?

Final Fueling Base
Closed Loop Target AFR
AF Correction #3

If so, try logging those, along with:

RPM
MAF (g/s)
Load (g/rev)
Accelerator pedal angle
Throttle opening angle
AF Sensor #1
AF Correction #1

My guess is that the first 3 will show the target AFR bouncing around, and the TOA parameter will show the idle control playing catch-up.
i'll grab a log tonight or tomorrow morning. i havent made it to pepboys to get maf cleaner

Also, if you stab the throttle while it's doing that, or if you try to drive, does it immediately go back to normal?

Mine does, which is part of the reason I think it's just an emissions thing. Idling with a cold cat is just about the most toxic thing your car can do. Other than WOT pulls with no cat, of course. :)
If i blip the gas once to about 2.5 or 3k it it will stop bouncing or if i drive it. exhaust is catless :devil: but i do have the stupid airpump if that means anything at all...
 

·
Registered
Joined
·
1,174 Posts
Sounds like the same thing, then. I suspect that this happens to a lot of Subarus with big injectors.

There's got to be a table in the ECU that controls it. It's not in the open-source ECU definitions yet, but Cobb might already have it. You'd have to check with your tuner.
 
1 - 19 of 19 Posts
Top