04 S4, Only 49K Intermittent Engine Lean Code

**ironchef1369** · 06-30-2008 12:20 PM

I've already searched the forums on the infamous P0171 - Engine Running Lean (Bank One) code and came up with a lot of things specific to the A4 and honestly a long list of things that could be bad. My car isn't under warranty anymore either.

I've got an 04 S4 with only 49k miles on it and its been intermittently throwing this code. It'll go on and off between tanks of gas.

The symptoms began when I ran the tank down to the gas light and then the check light came on about 30-40 miles right after I filled up again. Every time, if the gas light come on, the never fails, the check code appears. I figured, ok, i won't let the gas run down and then no light. Well, as of last week, light came on at 3/4 tank.

The car has been getting pretty horrible gas mileage as well. I am the second owner of the vehicle and when I first got it at 39k i was getting a good 18mpg average. Now i'm driving like a granny and lucky if i can eke out 14mpg. Im thinking the lean condition is causing my engine to run rich.

Anyway, I've read that the major things here are either a bad MAF or a vacuum leak. Any suggestions and/or the vacuum diagram for my S4? (the one under the hood is not really readable & peeling up)

Thanks in advance guys.

**91gl** · 06-30-2008 12:25 PM

change your 02 sensors

**ginkof** · 06-30-2008 11:05 PM

my car threw that code for a vacuum leak

**ironchef1369** · 07-07-2008 01:06 AM

Ok, update on the problem.

Took the car into Commonwealth Audi in Santa Ana and had the car diagnosed last week. As it turns out my car was running a full 17% lean in bank one. Explains power loss and mpg loss.

A first attempt at diagnosis resulted in a re-tightened intake manifold. Checked for lean condition, returned right away. Second attempt at diagnosis is a bad intake manifold altogether. After searching for vacuum leaks, checking all the oxygen sensors, the MAF, all the intake piping, the Audi service foreman suggested a full intake manifold replacement.

So, according to my Audi Service Manager, despite the fact the car is out of manufacturers warranty, this can be classified under a "emissions warranty." I didn't know there was a difference but I'm not complaining!

So, story right now is, car is at the dealer awaiting a new intake manifold which should be installed by wednesday. We'll see what happens...

**RAudi Driver** · 07-07-2008 07:39 AM

Nice that you're getting it for free. I just don't understand how an intake manifold could cause your car to run lean. Can someone explain?

**ChronicTeutonic** · 07-07-2008 09:27 AM

Intake is aluminum, right? Could be cracked due to a poor casting of the intake. Any vacuum leaks past the MAF will cause a lean condition since the MAF is telling the ECU "X" amount of air is incoming, yet the leak makes it "X" plus extra from the leak. The injectors are only supplying the amount fuel to match the MAF reading which isn't enough for extra air.

**ironchef1369** · 07-15-2008 06:22 PM

So the car's been at the dealer now for over 2 weeks and they still can't figure out what's wrong with the car. As of this point, the car has had the intake manifold replaced, the fuel injectors and injector seals, had the exhaust solenoids replaced and plugged (I have an aftermarket exhaust), and a reflash on my ecu. All of which, to no avail, have helped to solve the lean code issue.

From the latest fuel trim reading, bank two is now reading rich and bank one is still lean. I have no idea how the car can run rich on one side and lean on the other but thats what it is reading out.

Get ready to laugh, my service advisor told me that she has a tech going to "advanced engine management" class tomorrow and he is going to ask his professor for a point in the right direction! My service advisor suggested that we go at this one more time and if it can't be fixed, then take this up with Audi corporate and see what we can do.

Any ideas/comments/experience with Audi corporate?

**ngng** · 07-15-2008 06:37 PM

Originally Posted by ironchef1369

Any ideas/comments/experience with Audi corporate?

Your car is out warranty, there's not a whole lot Audi owes you. I'm surprised you got those replaced under an "emissions warranty".

**ironchef1369** · 07-16-2008 06:36 PM

^^ You're right, Audi doesn't owe me anything cuz i'm out of warranty...but i can hope right?

Tech is now trying to switch the injectors between banks to see if he can get the fuel trim to reverse its lean/rich status to the opposite side. If thats the case, I might need new injectors. (Above i said they had been replaced already, as it turns out it was just the seals) Sound like a plausible cause?

I've already run a ton of injector cleaners but perhaps they just have gone bad?

**iconoclast** · 07-17-2008 06:16 AM

post latest update... this is really odd problem, i am curious to know the outcome.

**ironchef1369** · 07-22-2008 05:55 PM

The Audi is fixed!

The latest update is:

Pulled out and tested the front O2 sensors, still good. Tested the rear O2 sensors, still good. Now going backwards to the easier stuff, changed out the fuel filter and the spark plugs and the engine lean/rich returned to spec without moving. Now, I am lead to believe that the following was changed and the root problem was just spark plugs and fuel filter??

1) New intake manifold (old had hairline crack, i'm assuming poor casting)
2) New fuel injector seals (after swapping injectors from side to side to see if the lean/rich condition swapped sides)
3) Exhaust valve solenoid replaced
4) Checked front and rear O2 sensors
5) Checked for vacuum leaks
6) Replaced fuel filter
7) Replaced all spark plugs

Having minor tune up issues would have somehow been more plausible had the engine not been running rich on one bank and then lean on the other. But apparently, it is fixed now.

I am now talking with the dealership on how much this lengthy diagnosis (3.5 weeks in the shop) is going to cost because I was told by my service advisor that they would not be charging me any hours of labor without my consent. However upon the phone call yesterday, she told me that the tech wants to charge for 5-6 hours of labor already. Clearly, I did not consent to further diagnosis and labor hours but in the end, the car was fixed.

Also, not to mention that the car has an extra 200 miles, and my gas tank is empty b/c of the tech driving it. Because the light was a long-term fuel trim issue, it took about 30 miles to come on.

What a long drawn out drama....

**charliemike** · 07-24-2008 10:10 AM

Originally Posted by ironchef1369

The Audi is fixed!

The latest update is:

Pulled out and tested the front O2 sensors, still good. Tested the rear O2 sensors, still good. Now going backwards to the easier stuff, changed out the fuel filter and the spark plugs and the engine lean/rich returned to spec without moving. Now, I am lead to believe that the following was changed and the root problem was just spark plugs and fuel filter??

1) New intake manifold (old had hairline crack, i'm assuming poor casting)
2) New fuel injector seals (after swapping injectors from side to side to see if the lean/rich condition swapped sides)
3) Exhaust valve solenoid replaced
4) Checked front and rear O2 sensors
5) Checked for vacuum leaks
6) Replaced fuel filter
7) Replaced all spark plugs

Having minor tune up issues would have somehow been more plausible had the engine not been running rich on one bank and then lean on the other. But apparently, it is fixed now.

I am now talking with the dealership on how much this lengthy diagnosis (3.5 weeks in the shop) is going to cost because I was told by my service advisor that they would not be charging me any hours of labor without my consent. However upon the phone call yesterday, she told me that the tech wants to charge for 5-6 hours of labor already. Clearly, I did not consent to further diagnosis and labor hours but in the end, the car was fixed.

Also, not to mention that the car has an extra 200 miles, and my gas tank is empty b/c of the tech driving it. Because the light was a long-term fuel trim issue, it took about 30 miles to come on.

What a long drawn out drama....

Here's my problem with the way these things are done ... It's obvious that they didn't know what they were doing so they just started throwing ideas at the wall to see if anything stuck. I do not think you should have to pay for a fishing expedition. You should pay the labor on the new filter in and plugs because that fixed your problem. I don't think that's unreasonable.

But doing $2000+ (guessing with all the parts+labor) worth of work to fix a $200 problem doesn't seem right to me.

I realize that's not how things work in real life but nonetheless that's my $.02 about the process.

**Tugboatguy** · 07-24-2008 11:56 AM

Originally Posted by charliemike

Here's my problem with the way these things are done ... It's obvious that they didn't know what they were doing so they just started throwing ideas at the wall to see if anything stuck. I do not think you should have to pay for a fishing expedition. You should pay the labor on the new filter in and plugs because that fixed your problem. I don't think that's unreasonable.

But doing $2000+ (guessing with all the parts+labor) worth of work to fix a $200 problem doesn't seem right to me.

I realize that's not how things work in real life but nonetheless that's my $.02 about the process.

Ya thats the problem with shops/dealerships these days, good ones have mechanics who can diagnose a problem starting with the simplest fix first(fuel filter was the obvious first step). Bad ones have parts changers(you change enough parts eventually you fix the problem).