Audifanatic007

Alright so this is the deal, I am not extremely advanced when it comes to cars, but I do know how to use a wrench if you know what I mean.

I have a 2003 audi A6 quattro 3.0L

I LOVE MY CAR..

So my CEL is on indicating random cylinder misfire a P300 code, on 2, 4, 5, 6... no drivabilty issues expect the very seldom rev at idle...

I changed all of my vacuum lines, my MAF sensor and the CP have been fixed along with usual maintenance of air filters and whatnot.

However, my vehicle still had the CEL light on indicating as well SYSTEM TOO LEAN BANK 2

Took the car to the Jacksonville, Fl Audi dealership (like 1:15 away from home) and spent a wonderful 5 hours there, they said that maybe a tune-up (spark plugs being changed, new fuel filter, fuel injector cleaner) should have her running like a champ.... given these seem like easy things to check (and I did check already but did not replace) I allowed the dealer to go ahead and fix her up for a cost of around 1G (painful). The dealer came out and told me, I have the CEL off no prob, she should be good. After 2 trips (exact number required to pull the code again) the CEL returns to the lit position. The techs at the dealer seem utterly confused and I will be making my second trip to them tomorrow...

So.... Does anyone have any idea what might be pulling the code other than:

Spark plugs
CPs
Fuel filter
Fuel Injectors
Vacuum Leak
CAT (no rotten egg smell)
Air filters
Mass air flow sensor

???


Any Help would be great since the dealer doesn't know....

radhaz

I think it's the rather over sensitive emissions system. My car does this all the time, and I just clear it when smog check time comes up.

PapatoeSC

i had the same issue and it was the Fuel Injectors
i had to replace 2 of them for $125 each
and the other 4 were reconstructed for $25
just remember this prices are in Mexico i dont know how much it would be in the US

Just Me

your left the oxygen sensors off your list. I'd think about them in two contexts:

1. a bad reading could cause a lean condition
2. the 02 sensor in fact measures whether it is lean or rich, via residual oxygen. So an 02 sensor out of calibration could simply be providing the wrong reading - either as an input or as an output

G

AR15Texan

Let me get this straight you paid $1,000 for a tune up?

"tune-up (spark plugs being changed, new fuel filter, fuel injector cleaner)"

Spend your next $1,000 on a VAGCOM and a laptop. Drive the car an monitor things like misfire and O2 sensor readings.

gmwaudi

A misfire can generate a lean condition code because if the cylinder is misfiring, it is not burning the fuel air mixture. Your misfiring cylinder is now an air pump making the pre cat O2 sensor read lean. It doesn't matter what the cause of the misfire is (fuel, ignition, base engine), the pre cat O2 will read lean. Remember that an O2 sensor reads oxygen; even if there is unburned fuel in the exhaust, it doesn't care. If the cylinder is misfiring, there will be excess oxygen in the exhaust causing the pre cat O2 to read lean.
It drives me nuts to see people throw parts at a problem hoping to make it go away. One way to diagnose this problem is to look at fuel trim and compare bank 1 to bank 2. If the fuel trim number is positive, it is adding fuel to compensate for a lean condition and if it is negative, it is subtracting fuel to compensate for a rich condition. I would suspect that bank 2 will have a positive relatively high fuel trim number. If that is the case, start looking for causes for a lean condition on bank 2. They replaced the plugs, what about the other ignition components for bank 2? There could be a vacuum leak and the best way to locate vacuum leaks is with a smoke machine. Fuel injectors can be tested for pressure drop and their electrical pattern can be checked with a lab scope to test the internal components of the injector. It sounds like the O2 sensor is just doing its job reporting the lean condition; I wouldn't replace it yet. An exhaust leak in front of the O2 can also cause a lean condition.
There has to be a competent shop in Fla. that can accurately diagnose your problem rather than adding more parts to your bill. good luck.