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Old 02-18-2018, 01:14 PM   #1
SpoolinSnail
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Default Engine struggles to find idle after acceleration

Year/Model: 2007 STi

Mileage: 130k

Issue: Car can't find idle

So I have been having issues with my car hunting for an idle, it got progressively worse and now it will stall after releasing the throttle if revs go over 3k. If i rev under 3k (say 2500rpm) the rpm's drop all the way down to zero, the car acts like it's going to stall (engine oil light, check engine light, abs, etc. all come on if it had stalled) and then it catches and shoots back up to over 1000rpm only to drop back down to below 100rpm and then it just oscillates back and forth until eventually it either stalls or the idle smooths back out. The car idles fine when first turned on but as soon as the throttle is touched it starts the cycle. I have cleaned and serviced the throttle body, replaced the MAF sensor ( car runs perfectly with it unplugged i.e. limp mode) and yesterday I replaced the fuel pump. The car never drops below 100rpm now but the idle still oscillates after hitting the throttle. I tried to drive it down the street to see how it did and within 100 yards I got a misfire in cylinder 1 ( later the misfire was in cylinder 4) Anybody have any ideas? The car isn't throwing any codes at an idle except P2431 & P2433 (which its had for over two years and only pertain to the secondary air pump). My next step is to replace the idle positioning sensor, which is conveniently integrated into the throttle body so if anybody has any other ideas before I source a new throttle body, please let me know.
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Old 02-18-2018, 11:49 PM   #2
Mgamer
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I'm having the same issue kinda, My car does idle but it's rough, it does sometimes catch a good idle but again will revert to the though idle with misfires that are audible. I'm currently checking the timing to make sure it didn't skip, Next step would be cleaning the MAF and doing a cylinder compression test, if I come across a fix i'll tell ya to see if it helps.
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Old 02-19-2018, 09:18 AM   #3
Samurai Jack
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Quote:
Originally Posted by SpoolinSnail View Post
Year/Model: 2007 STi

Mileage: 130k

Issue: Car can't find idle

The car idles fine when first turned on but as soon as the throttle is touched it starts the cycle.
This is because you are in cold start and you are getting cold start idle, which is normal. As soon as you hit the throttle, typically the idle will drop to what should be normal idle, but apparently not in your case.

Have you looked for vacuum leaks?
Have you cleaned your IACV?
Have you checked your Purge Control Valve to see if it is cracked?
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Old 02-19-2018, 07:05 PM   #4
SpoolinSnail
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Quote:
Originally Posted by Samurai Jack View Post
This is because you are in cold start and you are getting cold start idle, which is normal. As soon as you hit the throttle, typically the idle will drop to what should be normal idle, but apparently not in your case.

Have you looked for vacuum leaks?
Have you cleaned your IACV?
Have you checked your Purge Control Valve to see if it is cracked?
As far as I know 07 Sti's don't have an IACV, they are all DBW
Will have to check on the vacuum leak and purge control valve though, not entirely sure where it's at
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Old 02-20-2018, 09:33 AM   #5
Samurai Jack
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Quote:
Originally Posted by SpoolinSnail View Post
As far as I know 07 Sti's don't have an IACV, they are all DBW
Will have to check on the vacuum leak and purge control valve though, not entirely sure where it's at
Purge Control Valve should be right next to the alternator, on the left side as you are standing in front of the car.

You made me look ...
Looks like the IACVs are on the 1990 - 2006 models.
Couldn't find one listed for 2007

Hmm ... Looks like you may not have one of these either - VALVE-PRESSURE CONTROL - what I was calling the Purge Control Valve

Last edited by Samurai Jack; 02-20-2018 at 09:43 AM.
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Old 02-22-2018, 09:15 PM   #6
pouncingmailbox
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Quote:
Originally Posted by Mgamer View Post
I'm having the same issue kinda, My car does idle but it's rough, it does sometimes catch a good idle but again will revert to the though idle with misfires that are audible.
There must be quite a few of us having these problems. I have also experienced similar symptoms on and off over the past 2 years in my 2006 WRX wagon. In addition to the symptoms you describe i have found that I need to leave my key in the on position for ~5 full seconds before starting the car to give the fuel pump enough time to pressurize the system. If I don't do this it missfires quite badly and sometimes won't start.

Swapping out the spark plugs seemed to improve things for me about 1 year ago. But actually today the missfiring got quite bad on the highway whenever I pressed the accelerator more than gingerly. So I ended up taking it in to a professional as i was out of town and away from my tools.

My first thought was that it is the fuel pump failing... but i am surprised that you are still experiencing the missfires after replacing yours... I will stay tuned to see what the solution ends up being.
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Old 02-22-2018, 09:20 PM   #7
viper_crazy
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Quote:
Originally Posted by pouncingmailbox View Post
There must be quite a few of us having these problems. I have also experienced similar symptoms on and off over the past 2 years in my 2006 WRX wagon. In addition to the symptoms you describe i have found that I need to leave my key in the on position for ~5 full seconds before starting the car to give the fuel pump enough time to pressurize the system. If I don't do this it missfires quite badly and sometimes won't start.

Swapping out the spark plugs seemed to improve things for me about 1 year ago. But actually today the missfiring got quite bad on the highway whenever I pressed the accelerator more than gingerly. So I ended up taking it in to a professional as i was out of town and away from my tools.

I will update this if they figure it out. But i am guessing that the fuel pump is on its way out.
Fuel pump, but maybe the fuel sock is a bit plugged.
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Old 02-23-2018, 03:59 PM   #8
Mgamer
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Quote:
Originally Posted by pouncingmailbox View Post
There must be quite a few of us having these problems. I have also experienced similar symptoms on and off over the past 2 years in my 2006 WRX wagon. In addition to the symptoms you describe i have found that I need to leave my key in the on position for ~5 full seconds before starting the car to give the fuel pump enough time to pressurize the system. If I don't do this it missfires quite badly and sometimes won't start.

Swapping out the spark plugs seemed to improve things for me about 1 year ago. But actually today the missfiring got quite bad on the highway whenever I pressed the accelerator more than gingerly. So I ended up taking it in to a professional as i was out of town and away from my tools.

My first thought was that it is the fuel pump failing... but i am surprised that you are still experiencing the missfires after replacing yours... I will stay tuned to see what the solution ends up being.
I actually have that issue too! Although i thought of it as normal, I've read on this site https://www.highflowfuel.com/ there is a recommended "add-on" part that is a bigger check valve, this is what I assume would cause the "waiting for 5 seconds" part. I read up on it and it said it will instantly start the car, so I figured I'd share that with you incase it helps.
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Old 02-24-2018, 10:57 AM   #9
SpoolinSnail
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Did some research and saw more than a few people claiming their throttle positioning sensor was giving them issues. Ordered a new throttle body today, will update if it was indeed the throttle positioning sensor.
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Old 02-25-2018, 06:39 PM   #10
pouncingmailbox
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My similar issue turned out to be a dirty throttle body and a loose coil pack. Cleaning the TB and tightening the coilpack along with resetting the ECU solved my issue. But i see you already tried cleaning your TB.

Last edited by pouncingmailbox; 02-25-2018 at 06:46 PM.
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Old 03-16-2018, 04:42 PM   #11
SpoolinSnail
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New throttle body and changed fouled cylinder 4 plug and it runs like new
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