We have a 2001 1.8T with the AUG engine. About a week ago, wife was driving and got a cell - P0170 (fuel trim malfunction). Did some research around here on that (so I'd be educated when talking to someone about it), and made an appt with the dealer (was getting an 80K svc anyway).
Dealer ruled out the vacuum lines, check valves, and the MAF, so the O2 sensor was next ro check. Sounds like the same protocol most on PW would recommend. In the meantime, many more codes were being thrown (random misfires, etc), car was running like crap, no power on acceleration, etc. Dealer said all these new codes were probably a "snowball" effect off the original P0170.
Dealer removed the rear 02 sensor (behind cat), and said it was definitely toast, so they replaced it. When car is first started, it idles and runs great. Only when warmed up does it start spitting and sputtering. This continued even with the new 02 sensor in place.
Dealer removed the "brand new plugs" and put some kind of scope into the engine. Said there was evidence of "rust" on the pistons (said it looked like mushrooms - weird). However, there is no evidence of water/coolant getting in (except for the rust), head gasket apparently is ok, coolant level is fine, no white smoke out the tail, etc. In addition the last two Blackstone UOA's show no antifreeze, no water, insolubles at .2, and fuel % < .5, all very good. So where did the rust come from? Could it be a contaminated tank of gas? Last tank fillup was Sunoco, about 50 miles before all this started up.
Dealer pulled the fuel filter and said it looked pretty bad, so they are replacing that. They are also doing a fuel injection service/cleaning to see if that will help, since they are concerned about contamination in the fuel rails, injectors, etc. If not, they are suggesting dropping the fuel tank, and thoroughly cleaning it out. I guess this is all assuming that I just got a lousy tank of gas, and if so I guess the measures taken will remedy that.
I'm already into this for over a grand (incl. the 80k svc), and could be looking at a lot more. I have confidence in the dealer, and they are really trying to keep the costs down, which I appreciate.
My question to you guys - any of you ever seen anything like this, or have any ideas? I was sure when it first started that it was probably a vac line, or a dirty/bad MAF, or an O2 sensor at worst. Well the rear O2 was bad (as described above), but that appears to be effect and not the cause. Dealer said the bad O2 was "white" - not sure what that means. I fear the new O2 that was just installed will crap out in a few hundred miles if the root cause is not uncovered. But car is really not driveable safely right now anyway.
All ideas appreciated - TIA.