Jump to content

P0172, surging, rough idle, hard start


Recommended Posts

Thanks in advance for any help...I've searched the forum and nothing quite matches the issues I'm having.


2007 LGT Limited, 5spd manual, 105k miles, no mods, stock tune, running 93 octane gas from 2 different stations that I've never had a problem with.


In the last 3 weeks I've thrown a P0172 code twice, both happened while cruising at about 70 mph. Learning view showed no pulled timing, but A/F learning was -25 at 40+ g/s. After resetting the ECU there's a very noticeable surge/stumble (not the typical stuttering) under acceleration that get's better but doesn't go away as the car starts pulling fuel until the code comes back. The car is also difficult to start when it's been sitting for a few hours and it's warm out (ambient temp 70+) and there's always a rough-ish idle. Not a violent idle, but definitely noticeable in the car (more so than other Subaru's I've been in). I've recently replaced the O2 sensor, with no change in the symptoms.


I'm leaning towards the FPR, but I'm open to any and all suggestions. I can pull any logs that may help diagnose this problem so please feel free to ask for them. Again, thanks for any help.

Link to comment
Share on other sites

There are two O2 sensors. Which did you change ?


Clean the MAF and IAT sensors I used a dry Q-tip to clean mine. Be careful what spray cleaner you use if you want to do that.


You may have a sticky injector. A can of Seafoam in the gas tank may help.


At that mileage the timing belt is do, was it done yet ?

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.


Engine Build - Click Here

Link to comment
Share on other sites

I replaced the upstream O2, downstream shouldn't affect fueling? I cleaned the MAF and IAT tonight, but I haven't taken it out yet. I'll run seafoam through the tank tomorrow afternoon, need to fill up anyway.


Timing belt hasn't been done yet, but I have it in hand. That's slated for next weekend. While we're on that topic, should I go ahead and replace the water pump while I'm at it?

Link to comment
Share on other sites


This topic is now archived and is closed to further replies.

  • Create New...

Important Information

Terms of Use