So I have been chasing around a phantom vac leak/lean condition on my wife's B6A4 1.8TQM with 135K mi on it. It is running perfectly at this point but every time I clear the codes the P0171 comes right back. I replaced the PCV but when I finished the job I checked the outgoing part and discovered that it was fine but since I had it I went with it. I also changed the fuel filter recently with an OEM replacement and it seems to be doing fine. I am not hearing any adverse noise from the fuel pump but I haven't ruled it out yet either. Seals on the injectors seem to be fine but are a cheap and easy replacement too. Part of the reason I am looking at injector seals and/or fuel pump is that it will occasionally have a long crank time on start up as if the fuel pressure has not held while parked.

I can't hear any vacuum leaks and like I said it is running like a top but I haven't put a vac checker on it yet. I have been spraying all kinds of flammable stuff all over the vacuum tubes but haven't sensed so much as a raised eyebrow from the engine.

The MAF sensor element is clean but I have not done any other testing on it yet since I can't seem to find what the resistance values are supposed to be on it and I don't have access to a spare one to swap in and test that way.

I have decided that it might be time to check those inline check valves so I'm wondering. Assuming the tube size is correct is there any reason not to use the generic Dorman brand check valves from Autozone etc for $5/ea as opposed to the other ones from ECS or whomever for $35/ea.

I have been searching the forum for a month now and the check valves seem to be a likely answer for this code so I'm just wondering since there are 5 or 6 of them in the system.

 

Lots of people have had good luck with check valves from US Plastics, and they're way cheap.

 

 

Thanks guys, a damn tree fell in my yard last night and took out my fence so I wasn't able to play with it today. Hopefully I will have time to do some checking tonight. It's a relief to know I can just use the cheap ones.

 

So I just went for the propane test on the vacuum system and could not find any leaks. I did however unplug the MAF sensor with the car running and noticed that there was no change in idle except for a momentary drop in RPMS then the car just carried on as normal. From my searching it would appear to suggest that my MAF is bad. I think I am just going to bite the bullet and replace the thing.

Now I just need to get that tiny T9 torn driver so I can fix the self opening/closing moon roof and this car might just seem somewhat drivable again.

 

MAF sensor was changed out as was the Crank sensor and all seems to be well now with no lights or codes left.

Now on to the washer pump leak.