2005 WRX PPP - P0171 - Fuel Trim Lean
 

Hi,

I have a 2005 WRX PPP Wagon (2.0l) which has an engine light on. The car is completely standard (apart from the factory PPP) and has only done 25k miles. Car drives fine, maybe its slightly worse on fuel but nothing that obvious.

Ive connected ODB and looked at the error which states Bank 1 lean condition. After looking the error up it seems likely to either be a intake leak, MAF sensor malfunction or front O2 sensor.

I cleaned the MAF sensor, reset the error, reset the ecu (disconnected battery off for a while) and the error only reappeared 40 minutes into a journey.

I think I will try the O2 sensor next - Does anyone know the specific sensor type? I like to buy OE as Ive been stung several times by dodgy parts but if its just a standard DENSO item I can buy cheaper from a supplier thats known, ill just go that route.

Ive had a quick look for vacume leaks but without it being an obvious its difficult to tell. Is there a better way to check?

Also, its due a service soon. I would prefer a stamp in the book (of some description) so if anyone can recommend somewhere SE (preferably Hertfordshire areas) for a standard service.

When O2 sensors go they tend to flag up lambda or Oxygen sensor as the issue and run rich rather than lean in my experience. Lean would indicate air getting in somewhere after the MAF or there is a fuel supply problem to that bank.

My bug keeps throwing up the same code lately. But seems to come on when at idle not while driving it!

Had it about 4 times in the last 6 weeks or so

Ive had a quick check of the pipework after the MAF sensor and tightened a couple of the clamps up a small amount but cant see anything obvious.

I took some logs of the fuel trims, MAF and manifold pressure using an ELM327 ODB adapter. I tried every other free app for the device but they are all crap and the only app that did data-log, reported 2bar of boost when i accelerated quickly which cant be right? So not sure I trust the other readings...

At idle the app was reporting ~5psi.
At idle short term fuel trim swings ~2% lean/rich.
At idle long term was about 8%.
Under hard acceleration short term fuel trim was +25% (rich)

Ive bought Scan XL and will repeat the same when I get the licence.
http://www.palmerperformance.com/pro...lstd/index.php

I might get one of those boost leak testers and give that a go.

Sorted mine today hopefully, was an air leak but was my doing!
Luckily the engine did not grenade itself!!!

How did you sort it?