Idle Searching, 2007 STI

XSPWR · 10-10-2018, 10:20 AM

Idle searching, 2007 sti - YouTube

Video of my car searching for idle. It does this about 20% of the time when I let off the throttle at a stop. I just recently swapped out the throttle body thinking it may be the culprit. I have the idle set to 1000rpms because it will almost die when doing this if it's set lower.

Car has a Perrin topmount/rotated kit with a big custom ram intake, tuned entirely speed density (is this just something I'll have to deal with, it being SD?). Basically has everything that can be done to it. Perrin top feeds, id1000s, Perrin fuel regulator, TGV delete, Tial Q bpv, Turbosmart boost controller, built bottom end, etc. No head work.

Quite a few wires that have been tapped into under the dash by previous owners. It used to have a Hydra standalone and a hydramist setup, I'm wonder if possibly one of the wires were damaged by the splicer/vampire clips they were using...

Any other ideas?

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Turpid Porpoise · 10-10-2018, 10:59 AM

Have you tried to boost leak test? A vacuum leak can cause a hunting idle. You may also want to check your injector orings, if one is nicked it can cause just enough of a vacuum leak to create this issue.

XSPWR · 10-10-2018, 01:22 PM

I did perform a boost leak test and it held fine up to the 20psi I was comfortable with pressurizing it to. I'll look into the ORings, didn't think to look there.
Weird thing is, most the time it idles fine. I do find that occasionally shifting from gear to gear it will hesitate, only at very low engine load though...

Turpid Porpoise · 10-10-2018, 03:50 PM

Check your grounds while you are at to help rule out something simple.

Make sure your fuel pressure is properly set and you can check fuel pump voltage to rule that out as well.

When did this start and what changes were made prior to this occuring? If no changes were made was there anything out of the ordinary that you can think of that happened around the same time?

XSPWR · 10-10-2018, 07:16 PM

I bought the car recently. It was having issues originally and needed a new engine harness and ecu (harness had multiple wires melted together arcing, popped the ecu). Thing runs like a top when at WoT or just cruising, literally only issues are at idle or when shifting at low speed with the engine cold.

I'll go through and check out all the grounds as soon as I can.

SwappedHawk · 11-28-2019, 07:02 PM

Pm ed

stoich68912 · 11-28-2019, 09:34 PM

I have an 07 that does the same thing, extremely intermittent. 90% of the time it idles rock solid and like you, the car runs great otherwise. I recently swapped injectors and added flex fuel stuff and still caught it hunting idle once for a few seconds. Logs show nothing weird, no leaks I could find along with freshly seated injectors I'm kind of lost myself.

I'm still on a MAF-based tune, so no SD for me. The similarity I do see is all the spliced/tapped wires under the dash. I've been meaning to get under there and sort it all out so I, too, wonder if something there could be the cause.

EDIT: And...this is an old thread...

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10-10-2018, 10:59 AM	#2
Turpid Porpoise Scooby Specialist Member#: 476573 Join Date: Oct 2017 Chapter/Region: MAIC Location: Lovettsville, Virginia Vehicle: 2008 Impreza WRX STi Silver	Have you tried to boost leak test? A vacuum leak can cause a hunting idle. You may also want to check your injector orings, if one is nicked it can cause just enough of a vacuum leak to create this issue.

10-10-2018, 01:22 PM	#3
XSPWR Scooby Newbie Member#: 418247 Join Date: Apr 2015 Location: Billings, MT	I did perform a boost leak test and it held fine up to the 20psi I was comfortable with pressurizing it to. I'll look into the ORings, didn't think to look there. Weird thing is, most the time it idles fine. I do find that occasionally shifting from gear to gear it will hesitate, only at very low engine load though...

10-10-2018, 03:50 PM	#4
Turpid Porpoise Scooby Specialist Member#: 476573 Join Date: Oct 2017 Chapter/Region: MAIC Location: Lovettsville, Virginia Vehicle: 2008 Impreza WRX STi Silver	Check your grounds while you are at to help rule out something simple. Make sure your fuel pressure is properly set and you can check fuel pump voltage to rule that out as well. When did this start and what changes were made prior to this occuring? If no changes were made was there anything out of the ordinary that you can think of that happened around the same time?

10-10-2018, 07:16 PM	#5
XSPWR Scooby Newbie Member#: 418247 Join Date: Apr 2015 Location: Billings, MT	I bought the car recently. It was having issues originally and needed a new engine harness and ecu (harness had multiple wires melted together arcing, popped the ecu). Thing runs like a top when at WoT or just cruising, literally only issues are at idle or when shifting at low speed with the engine cold. I'll go through and check out all the grounds as soon as I can.

11-28-2019, 07:02 PM	#6
SwappedHawk Scooby Newbie Member#: 508112 Join Date: Nov 2019	Pm ed

11-28-2019, 09:34 PM	#7
stoich68912 Scooby Newbie Member#: 350291 Join Date: Mar 2013 Location: Darlington	I have an 07 that does the same thing, extremely intermittent. 90% of the time it idles rock solid and like you, the car runs great otherwise. I recently swapped injectors and added flex fuel stuff and still caught it hunting idle once for a few seconds. Logs show nothing weird, no leaks I could find along with freshly seated injectors I'm kind of lost myself. I'm still on a MAF-based tune, so no SD for me. The similarity I do see is all the spliced/tapped wires under the dash. I've been meaning to get under there and sort it all out so I, too, wonder if something there could be the cause. EDIT: And...this is an old thread...