kiciu

hello all.
the car : '99 A6 Q 2.8 automatic
P1129 Long Term Fuel Trim B2 system too rich
P1141 Load calculation cross check range/performance.

No rough idle however the transmission would hold gears till higher than normal rpm/speed
tip mode was fine.

2 days and 3/4tank of fuel later the CEL went off on its own .Car runs fine no more tranny hang

i know these 2 codes are MAF/purge valve related but could bad gas do something like this?
or tank overfilling?

I don't have Vag-Com to do MAF readings but I would like to know if it's on its way out.
Thanks everyone

kiciu

update :
CEL is back on with the same 2 codes and symptoms
is my MAF bad?

is there someone in central CT with a vag-com that would help run a test on my car?

thanks

SloopJohnB@mac.com

Yes, overfilling a tank radically and repeatedly can cause evaporative emission control problems and the resulting CEL. One possibility is a fueled activated carbon/charcoal canister...raw gas enough of it gets into the carbon canister and won't get out/ruins the canister.

OTOH, it may be something as simple as an 02 sensor, probably the B2 one in front of the cat.

kiciu

thanks for the reply
i gave the car to my roommate and he said he didn't overfill it but i saw some spillage on the side of the car ,not much maybe a 8" stain but enough to make me think of the possibility. however if he did it would be just this one occasion

i changed a couple of vacuum hoses and cleaned the MAF with maf cleaner during the 2 days the CEL was off and i'm pretty sure i didn't leave anything disconnected but i will check again in a couple hrs when it warms up a little

i dont mind changing the MAF or the O2 sensor but i want to be smart about it and not just throw parts at it

Wish i had the vag com....
what i can't explain is why did the CEL go off on it's own

SloopJohnB@mac.com

The other standard problem to search for is a broken or leaking vacuum line between the mass airflow sensor and the engine.

Logic says that such a leak allows unmetered air but the computer only sees what the MAF reads so the engine would run lean...more air, same fuel. OTOH, the 02 sensor sees excess oxygen so it richens the mixture and maybe throws a code for long term richness.

A google search revealed one guy had low coolant that caused problem. LOL...I see no logical correlation to low coolant and this code.

For a car with high mileage 02 sensors are the most likely cause. Pre cat sensors rather than post-cat since the precats are the ones that control the engine...the post cat sensors are used to evaluate the cat's performance.

kiciu

It warmed up a little bit and i was able to visually check the car .
with the car running i unplugged the MAF and plugged it back in a few secs later.
the only difference was that when i plugged it back in the idle would drop around 50ish rpm for a split second enough to be able to hear the different tone and then it would go back to normal .

it runs smooth and the tranny hang seems to be gone also . the car runs normal and the computer doesn't show a drop in milage not really sure how accurate it is ..

im thinking maybe there's a bad electrical contact somewhere which could possibly explain why the CEL went off on its own 2 days later and then back on a day after I cleaned the MAF and replaced a couple a vacuum lines.. maybe i disturbed something

I did have a somewhat low coolant level but i added some and got the level back to normal . only took about a 3rd of a quart maybe even less

i could go to a shop and have it tested but i think the $80 or so could go towards the actual part