P0171/Cold idle problems

I figured I would post this up for some advice and to hopefully give some more information to owners reporting a cold idle problem.

 

I too was suffering from the cold idle problem where the vehicle would idle fine until the blue light went off, then the idle would get lumpy for awhile, until the block was warmed up. Some people suggested intake manifold gaskets/o-rings.

 

Well I threw a P0171 code on my way home from class today. The CEL came on, TC light on, SI-drive flashing and cruise flashing. (I thought this was supposed to mean the vehicle is in limp mode, but it was driving just fine for me, despite lighting up like a Christmas tree.)

 

I have seen some people mention ideas like a vacuum leak, MAF sensor or O2 sensor. My car is going in to the dealer on Thursday for some normal maintenance and to have the clunk looked at in the front end, I figured I would have them look at this issue while it's in there as well. I did want to do some digging on it myself first though. Is there a diagram or a way someone could explain which lines I should be looking at under the hood? I read that there is a "T-line" under the intercooler, I assume I would need to remove the IC to get to it? Then I can just trace those lines to wherever they go and check every connection along the way? My buddy up here mentioned he has the stuff to do a leak test on it because he had to do it on his WRX. Would it be easier to just take him up on this offer?

i didnt think 07+'s have the T under the IC, from what ive read (i could be wrong though). you talkin about subaru Tim?

Take your buddy up on his offer. It'll make finding the leak a whole lot easier. Intake manifold gaskets would be my guess though as I had the same symptoms.

Intake manifold gaskets caused mine to do the same thing last winter.

Intake manifold gaskets caused mine to do the same thing last winter.

That's what I was thinking with mine. I have had the rough idle since last winter, but I never threw a CEL with it so I figured there's not much my dealer could have done about it. Now that I actually have a valid CEL, I figured the dealer could be of some use. I explained to the guy on the phone that I pulled the code, but I didn't want to sound like that "know it all customer." He gave me the typical "yea, but we need to do our own scan and diagnostic of the problem anyway." I hope they don't waste my time BSing around with the car. It goes in Thursday, so hopefully they'll find the issue then.

 

i didnt think 07+'s have the T under the IC, from what ive read (i could be wrong though). you talkin about subaru Tim?

Yep, I thought Foley had the equipment to do a leakdown test, but I don't think he does.

 

Can anyone confirm or deny whether the 2007+ has the "T" under the intercooler?

P0171= system lean, meaning too much air or not enough fuel. Yes, it could definately be the intake gaskets. I had similar symptoms with mine last year. Not sure whether yours has the tee or not. Are you boosting higher than stock? If so, it probably pushed a vacuum line off.

P0171= system lean, meaning too much air or not enough fuel. Yes, it could definately be the intake gaskets. I had similar symptoms with mine last year. Not sure whether yours has the tee or not. Are you boosting higher than stock? If so, it probably pushed a vacuum line off.

 

Yea, I'm boosting 17lbs, so a vacuum line popping off was a first thought of mine.

 

I was actually reading about this happening to people right before I got into my car to head home from campus, and then bam; it happened to me.

 

I've had the rough idle since last winter, but I never did anything about it (no CEL and it went away when the weather warmed up.) I wonder if this code is related to it at all. From all the threads I've read, a P0171/lumpy idle go hand in hand. I wonder why the rough idle never threw the code earlier. I'm wondering if the negative temperatures lately contributed to it. Hopefully I'll know on Thursday.

20 degrees or below is about when my CEL will kick in with P0171. Had my car in for his code last year and they re-flashed the ECU with new software. Was fine until this winter. Now the CEL will come on after warm-up and at idle (tad rough idle.) I'll park it overnight and it's cleared itself. Been pretty cold in Chicago so I haven't gone digging under the intercooler yet. Gonna play it safe and take it to a buddy at Subaru Libertyville this Thursday to see what they think.

intake manifold gaskets. mine did the same thing up untill a few weeks.

I have the same issue on my 07 Spec B. I searched all over the place for the vacuum T, only to learn that the 07+ does not have it. Mine idles rough typically when its under 25c, untill fully warmed up.

A lot of people think it seems to be a vacuum leak and pointing the finger at the intake gaskets, i wish someone would post a walk through or some pictures of getting to them and how difficult a job they are to change?

Well the code cleared itself, but it should be stored in the ECU for the dealer to find.

 

Hopefully they check out the intake manifold gaskets first on it. I'll let you all know what they find.

^ same happened here. Been +20 degrees lately. Let us know what the dealer says.

What idiots at the dealer. They found my clunking (broken endlink and bushings, just like I thought.) They are covering that under warranty, so I figured I would just have them fix it while it's there, instead of going with aftermarket links (the part's in stock.)

 

Back to my lean condition; they didn't find anything wrong with the car. The code cleared itself but was stored in the ECU. He said it was -4f when the code appeared. His excuse was, "in these cold conditions the vehicle can't handle all the air and tries to dump more fuel in to compensate and you got the CEL." I told him this doesn't make sense and I politely asked if they would look for leaks, particularly at the IM gasket. He said my car was idiling fine and there is nothing they can do for it. They're charging me an $85 diagnostic fee for the damn thing as well, because they couldn't find anything wrong.

 

This just confirms why I never take my cars to dealers when I can avoid it. I'll just deal with it once I get back down to New York and actually have my Subi independent shop working on the car.

I took mine to the dealer 4 times for the code before i said F it and did it myself.

I took mine to the dealer 4 times for the code before i said F it and did it myself.

That's my plan now as well.

 

This has just been one trip with the dealer. It slipped my mind to tell them to use synthetic, which I've been using for almost 70K now. At least they said they would make the change for me.

Back to my lean condition; they didn't find anything wrong with the car.

 

My dealer said the same thing at first. I told them that the engine had to be stone cold before the problem would occur. If they started it at any point and shut the car off, the problem couldn't be reproduced because the residual heat was enough to make something expand. At least my dealer kept the car overnight and tried again the next morning, at which point they were able to reproduce it and said the problem was exactly what I said it would be.

rip off.... what gasket are u changing?

intake gasket o-rings. http://www.fredbeansparts.com/index.php/subaru-intake-manifold-to-tumbler-valve-gaskets-1.html

Hey there. My car just started doing the same thing. Threw p0171, rough idle, stalls at stops, tells me to put my brake down(?) and such. Interesting thing for me is my wideband tells me my AFR is 16-20! I get some slight hesitation at no real load on highway but no issues when accelerating.

 

Same thing?

 

Thx.

 

By the by I'm not stock. Uprated turbo, injectors, headers, exhaust etc.

Quick question for those that have had this done: Are the gaskets in question between the intake manifold and tumbler valves, the tumbler valves and the heads, or both? Just making sure before I order parts.

 

TIA.

intake manifold to tgv.