Please help me understand.

[BigRod]

I have been using AZ for months to educate myself, but I have no real mechanical education, so please forgive me if I sound like an idiot. I've had my 03 A4TQM for about six months and I decided to save money and work on it myself.

I had a CEL, VAG-COM gave me the following codes:
2 Faults Found:
17519 - Oxygen (Lambda) Sensor Regulation: Bank 1: System too Lean
P1111 - 002 - Lower Limit Exceeded - Intermittent
17544 - Fuel Trim: Bank 1 (Add): System too Lean
P1136 - 001 - Upper Limit Exceeded
Readiness: 0000 0001

Also under Instruments I get:
01039 - Coolant Temperature Sensor (G2)
30-10 - Open or Short to Plus - Intermittent

After hours of serching AZ and other forums I decided to run these LOGS:
http://spreadsheets.google.com/pub?k...8WRipE0VrtLNTg

After I ran the logs I spent several more hours searching the forums, and have come to the conclusion that I either have a boost leak (most likely), a bad coolant temperature sensor (also likely but probably not related to the engine fault codes), or a bad O2 sensor (not likely, but it was in a thread somewhere).

So my question is, am I close? Or am I way off? If I have a boost leak wouldn't it be more evident on the channel 115 log? And why can't I find the boost leak? When I try to wrap my head around it, I figure that if I have a boost leak somewhere, more air would be getting in than what the ECU is reading, causing more air than fuel, which equals lean. Am I even on the right track? As I said before, I am new at this, and what little I do know comes from forums, so please feel free to talk down to me. Thanks in advance.

[Undisputed]

I'm no mechanic either. But check this thread. Someone got similiar codes to you and it was a boost leak. There are a couple of suggestions on the first page of the thread about how to check it. It's a long thread but it may help.

http://www.audizine.com/forum/showth...=227741&page=2

[BigRod]

Thanks for the link. I took another look and still can't find a leak, but I'm not looking hard enough. I'm going to fab up this boost leak tester http://www.audizine.com/forum/showthread.php?t=189114 and do a more thorough inspection. I cleared the code before I did the log, and the CEL hasn't come back on. I'm thinking it must be a small intermittent boost leak, which is why the lambda corrections are high when the turbo first spools, then level out. My theory is that air shoots out with the initial increase in pressure but because the leak is small less air comes out when the pressure is staying the same, even though it's possitive in relation to the atmosphere. But that is a total guess, and I'd like to know if my reasoning is anywhere near reality. What I need is either ten years of experience, formal mechanic training, or a week of hanging out with Old Guy . Thanks for the help, I'll post what I come up with.

[old guy]

Most likely you have a small vacuum leak somewhere. There are two types of fuel trim codes one is an "additive" code and the other is a "multiplicative" code. Yours is an "add" code which indicates that the ECU is only adjusting at idle. A "Mult" code indicates a problem across the full range and the ECU is adjusting constantly. Sometimes the coolant temperature sensor can play a part by sending false temperature info to the ECU but in your case I'm betting it is just a small leak somewhere.

Good luck!