Thought i would post what I believe to be a successful fix to a P1127 CEL code I got.

My '98 A4 1.8T quattro would have an intermittant stumble, idle fluctuation and when it got bad would through a CEL. I had it scanned at Advance auto and they said it was a P1127. Sometimes it would go away after a couple of start and the car ran ok. But if I was driving the car all day like running errands it would come back.

First I changed plugs which didn't fix it. After reading this board I started searching for vacuum leaks. I noticed that the hose connecting to the fuel pressure regulator looked shabby and replaced it. That didn't work. Then I noticed that the crankcase breather tube which sits underneath the intake manifold was cracked.I replaced the crankcase breather hose (it was a pain) which seems to have fixed the problem.

What was interesting is that after I fixed it the car ran very poorly at first, it didn't want to accelerate. It was acting as though it was running out of gas. But the more I drove it the better it ran. I think that this occurred because the vacuum leak caused the fuel pressure regulator to run to rich, the ECU detected the rich condition and trim the fuel schedule back. So once the vacuum leak was fixed the control was now running to lean. The moral of the story is to when you get a CEL check for vacuum leaks first they are probably your cheapest fixes.