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Old 09-04-2010, 01:07 AM   #1
Scooby Newbie
Member#: 139019
Join Date: Jan 2007
Chapter/Region: RMIC
Location: Utah
2005 Impreza 2.5RS
Obsidian Black Pearl

Unhappy Idle problems

Alright guys I know its been ages since I've logged on or seen any of you I've been so damn busy with work/family the last year its been crazy! My apologies for not making TT recently. Anyway, my car is having problems after buying a new battery and I'm in desperate need of your wisdom! So, my car dies when coming to idle after moving. It starts right back up with no problems, and runs great other than when I'm coming to a stop the idle RPM drops so low the car dies. It threw a CEL the day I got my new battery after about 20 miles (Low Idle RPM) and I've been told this is common with subies after replacing the battery, and that it should fix itself after "a few drive cycles" (some guys at Nate Wade told me this). After 3 days its still doing it. A year ago I had pulled my negative to reset my ecu and remember it giving me the same idle problems then, but it cleared up after about 10~15 stops, so I tried that yesterday. It's still having idle issues, but I haven't seen a CEL yet. It's becoming quite the pain in the ass having to start my car at almost every stop I make so any suggestions would be much appreciated!

Info: 2005 Impreza 2.5RS with 54k miles, custom cat-back exhaust, K&N filter with custom snorkus mod (). New battery is a Duralast Red-Top (Autozone).

PS: I searched for like 30 minutes on nasioc and rs25.com for any related problem before posting this and couldn't find any answers
other than IACV problems which I haven't ruled out completely, but I find it unlikely based on me just replacing the battery. :\

Thanks in advance for any input!
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Old 09-04-2010, 01:50 AM   #2
Scooby Guru
Member#: 154117
Join Date: Jul 2007
Chapter/Region: RMIC
Location: Midvale, Utah
2003 Forester


That's weird sounds to me like it's a possible bad ground. I would try a new/diff battery or test the current battery to make sure you have enough juice.

Where the hell have you been man!?! I read what you posted above but seriously that's no excuse! Good to see you still have your Subie and that you are still alive!
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Old 09-04-2010, 01:55 PM   #3
Scooby Specialist
Member#: 183634
Join Date: Jul 2008
Chapter/Region: RMIC
Location: At the "B"
02 wrx/ 92 ss
Booze fueled :)


Yeah I'm thinking iacv is dirty and sticking, if you haven't cleaned it yet is start there
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Old 09-05-2010, 01:48 AM   #4
Scooby Specialist
Member#: 81106
Join Date: Feb 2005
Chapter/Region: RMIC
Location: SL,UT
2014 Baby Mobile
Whitey White


Originally Posted by 907Bum View Post
Yeah I'm thinking iacv is dirty and sticking, if you haven't cleaned it yet is start there
Exactly. Make SURE you get a new gasket though, do not ever reuse an old IACV gasket.
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Old 09-23-2010, 09:01 PM   #5
Scooby Newbie
Member#: 127044
Join Date: Sep 2006
Chapter/Region: TXIC
Location: Austin, TX
2005 STi WRB w RPF1s


shaz, good to see that you are around man, GL gettin this fixed!
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Old 09-25-2010, 01:36 AM   #6
Scooby Newbie
Member#: 132839
Join Date: Nov 2006
Chapter/Region: RMIC
Location: Salt Lake City
2009 WRX


I had a 2005 2.5rs as well. Here's the deal, on the 2005+ 2.5rs Subaru threw the MAF sensor back on the RS along with the drive by wire throttle that comes with the 32-bit ecu.

The problem is most likely your custom snorkus mod. It's actually a helmholtz generator. It cancels out strange frequency resonation in the air so that the MAF sensor can get a clean and accurate reading. When you modify or remove it, the car will usually get a rich patch below 1,500 rpm.

So, why did this happen after you changed your battery? Easy. Subarus have a really awesome ECU that will learn over time to adjust to things. It will try to learn to adjust it's MAF and air fuel ratio in order to reduce knock, and run closer to the desired air fuel ratio (to a point). When you remove the battery, it starts off at square zero. It has to relearn everything. For whatever reason, it sounds like your car is really struggling to learn how to run correctly with the snorkus delete, or it has maxed out the amount of learned adjustment that it can make.

I would suggest that you return the intake setup to stock. When I had my 2.5rs, I thought the same thing and removed the snorkus section from the intake. After a fair bit of logging and comparison, I discovered that you actually loose a small amount of power by removing the snorkus or modifying it. This was especially noticeable in the low end. There was a bogged rich patch.

This cant really be tuned out either. The MAF incorrectly reads the amount of air coming in. It thinks there is more air than there actually is because of the turbulence. If you log the MAF voltage, you'll notice there's a bunch of crazy spikes and ditches in the sub 1,500 RPM range.

Try to return the intake to stock. Reset the ECU again. Give it a couple of days. If the problem still persists, it quite likely is something else.

Good luck.
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Old 09-27-2010, 03:09 AM   #7
Scooby Specialist
Member#: 199635
Join Date: Jan 2009
Chapter/Region: RMIC
Location: Provo, UT
02-4 rSTI


and in the mean time just give it a little heel-toe at the stops so you're never quite at idle, had to do that with the 240 all the time before i fixed some grounds and stuff.

oh, check your grounds. always a good place to start.
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