Bank 1 lean code- Check engine light- More service

[bmwpower603]

Just got my a check engine light on my 04 s4.

Code 0171: system to lean bank 1

I have noticed that my car doesn't idle perfect at all.

And I have some aftermarket exhaust clamps from when my mechanic did the clutch.

Could this be a combination of bad 02 sensors, and possibly spark plugs?

When i got the car inspected a few months ago, they said there was a "misfire" code. But i never even got a cel for it…


Any thoughts???

[d.m8ty]

I have the same thing happening but on bank 2


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[jakeoboy67]

intake manifold bolts coming loose abit ?

[bmwpower603]

That would be strange. But I guess easy enough to check. Am I still able to drive the car daily like this? Would this also cause idle to erratic on occassion?

[VinnysS4]

from what i have researched. Lean = leak. usually it means you have either an intake manifold leak or a vacuum leak, Either way, the O2 sensor is reading that their is too much air coming through the engine for the amount of fuel being supplied( ECU reads the air coming in and adjusts the injectors for the amount of air coming in. the O2 sensor reads the air coming out and adjusts the system for emissions. if it reads one side is lean or rich, it throws a CEL). This air is making its way into the system after the MAF sensor and at/before the O2 sensor. Could be a vacuum hose, intake manifold loose bolts, bad manifold gasket, exhaust manifold gasket, leaky exhaust before the O2 sensor, Bad O2 sensor, Bad MAF sensor...etc.. Grab a can of carb cleaner and lightly spray around the intake manifold and the vacuum lines around the Bank 1 side (side that has cyl #1) If the idle increases, you have located a leak. Fix said leak.

[bmwpower603]

Ok, so it's either the intake manifold. Or intake boot/ vaccum leak. I'll spray some carb cleaner tomorrow. If I get no change in idle. I'll assume it's an o2 sensor. Either way, should I bring this to audi to diag? Or my local audi mechanic?

[VinnysS4]

whoever you are more comfortable with. I prefer my local german shop that specializes in audi repair over the dealer. They have seen it all and the hourly rate is like 40 dollars an hour less then the dealer. That and the audi dealer is like 40 miles away...that helps. If the engine is running a little rough as well, it could be a vacuum problem. Have you ran VCDS on it to see what it says?

[bmwpower603]

I do not have VAG. I have a universal autel. (I would be up for purchasing one though) The RPM needle will move up and down slightly, and you can feel it in the car. It has a leaky engine mount, I just figured thats why it never felt smooth at idle.

As far as vcds. I do not know how to use one, and have only seen it on one website. For like $600.00. That's a bit much. IMO

[Brettannica]

This might be from Left field. How does it idle when you remove the oil cap? Does it start sucking?
I had a lean bank code on mine, and a rough(ish) idle and it turned out to be the PCV. That said, Baggio kept having a similar issue.

http://www.audizine.com/forum/showth...ystem-Too-Lean

[getslideways]

Not all codes will illuminate the CEL
Unmetered air entering the engine will cause the car to run funky
The intake system is made of dissimilar metals, so its no uncommon for the bolts to need re-tightening

Unlikely the MAF as you would get the lean code for both banks, HOWEVER Drifleft had a maf problem that started out as just showing one bank then eventually displayed both: http://www.audizine.com/forum/showth...74-P1138-FIXED!!

Have you tried unplugging the maf completely to see what the idle does then?

[bmwpower603]

Ok I just went out to check the bolts. I DO NOT have a 5mmallen (I DO have 6mm as said in many DIYs) Its not 6. its 5. SO cannot get to most of the bolts. But the TWO on the front part of the intake manifold I could tighten with my finger. I am off to get a 5mm allen, and tighten the rest. Am i able to tighten these with the fuel rail in the way? Or do I need to take some stuff off?

[VinnysS4]

They can be gotten with the rails on, I've done it. The Ross tech vag Com cable I bought was 375 shipped. Works wonders. I'm not 100% on using it yet, but it has already paid for itself in diagnostic fees from a shop

[bmwpower603]

All of the 5mm hex bolts were loose on my intake manifold. I tightened them up. And cleared the code.. Hopefully this will solve the issue.
**update
After clearing codes. I started the car. And the idle seemed lower than usual. It was at 3k rpm instead of 4k rpm. It eventually went nack uo to 4k. Does this lead to something?

[Lucca M]

It can be exhaust leak. Are you on stock tune? If yes. Check for exhaust leaks. When i had my stock ecu and stock downpipes flex pipes were bad and were leaking that caused my car to get lean code and bad idle. It also can be maf sensor, unplug it like someone above said and see if car will die or still run.

[bmwpower603]

My exhaust is rusted to shit. And my mechanic had to replace clamps in a couple sections, after doing the flywheel. Any suggestions on an affordable exhaust ?

[VinnysS4]

not too many affordable options out there. Better to just go with a reputable company like JHM. These cars don't like cheap. And di i read it right....your car idles at 3k rpms???? might want to get that looked at

[bmwpower603]

Once I tightened the bolts, and cleared the code. It was at 3k rpm, and slowly went up.

[bmwpower603]

Once I tightened the bolts, and cleared the code. Started the car, and hung at 3k-3.5k then went to normal.. Still have yet to unplug maf to see if it shuts off. Is it supposed to shut off?

[jakeoboy67]

All of the 5mm hex bolts were loose on my intake manifold. I tightened them up. And cleared the code.. Hopefully this will solve the issue.
**update
After clearing codes. I started the car. And the idle seemed lower than usual. It was at 3k rpm instead of 4k rpm. It eventually went nack uo to 4k. Does this lead to something?

What ?

[VinnysS4]

mine idles at like 700 rpms lol im confused

[bmwpower603]

I'm sorry. I'm way off on the rpm. It stayed at 600rpm, and slowly went to 800

[VinnysS4]

oh lol.

[bmwpower603]

Drove over 50 miles on cleared code. CEL hasn't come back yet!!!

[VinnysS4]

mine comes on every like 3 or 4 days for that code as well. might give it a few days

[bmwpower603]

Yours still comes on? Did you find the problem with yours?

[JimmyBones]

Very common problem. If I were you then I would take one intake manifold bolt out at a time, apply blue locktite to the threads, reinstall + torque to 11 Nm, repeat for all the other bolts, and double check that they are all tightened to 11 Nm. The blue locktite seems to help drastically.

[VinnysS4]

absolutely i agree with jimmy. Mine started to show up after i removed the upper and lower intake manifold. Im assuming its just a leaky gasket. I just haven't had the time to dig into it with my work schedule and xmas shopping. I clear the code and it comes back after a few cold starts. I might have an exhaust manifold gasket that's starting to leak and that could be it as well. When i get onto it i can hear it near the passenger side of the engine.(pretty sure its not intake noise either) i could always be wrong though

[VinnysS4]

see it went off again. I think my car throws the code when it is mad at me. haha. I'll be fixing it as soon as i fully recover from my accident

[0396]

Just got my a check engine light on my 04 s4.

Code 0171: system to lean bank 1

I have noticed that my car doesn't idle perfect at all.

And I have some aftermarket exhaust clamps from when my mechanic did the clutch.

Could this be a combination of bad 02 sensors, and possibly spark plugs?

When i got the car inspected a few months ago, they said there was a "misfire" code. But i never even got a cel for it…


Any thoughts???

Funny as I have the same intermittent "check engine light " when I scanned it it also shows lean on bank 1...now this occurred after I replaced both O2 sensor. I tried all the above suggestions and finally gave up. Now I simply rest /clear the code or simply let it reset it's self. Good luck with your search. Oh my S/4 is a late production 04 too.

[bmwpower603]

Its been over a week! Lean BANK 1 code solved. Every single hex screw holding down my intake manifold was loose. Tightened, and cleared code!!

Thank you AZ!!!!!! :D

If it comes back. Im getting manifold spacer kit from JHM, along with oil check valve kit!!!!!!