I have a 2000 a4 1.8t and when i start the car after its been sitting it misfires. After about 30 seconds its idles out but i have noticed a loss of power and it misfires once in awhile when im driving. I pulled up the OBD code and it showed up a P1128 which is manufacturer controlled. I looked it up on the internet and it said it was " Long Term Fuel Trim Multiplicative, Bank 1 System Too Lean " I was wondering if anyone knew what the problem might be and if there is anything I can do to try and fix the problem, before I would have to take it to the dealer.

 

P1128 bank 1 system too lean look for inlet/exhaust leak, AIR system/ hose leaks

 

If not a vacuum leak , check the O2 sensor.

http://www.obd-codes.com/trouble_cod...agen/index.php

 

I just went through the exact same problem. My car is a 2000 Audi A4 1.8t Quattro - Engine Code is ATW. It was also idling very rough (bouncing from 800 RPM down to 400 RPM like it was going to quit - especially in HOT weather with the AC on). Talked to ECS Tuning and they suggested the Oxygen Sensor and MAF sensor as I have 69,000 miles. After checking this forum and hearing it could also be anything from air cleaner, vacuum hoses, injectors, fuel filter, fuel pump, etc. I decided to replace the easiest stuff first. I replaced the Air Cleaner and put in new spark plugs. I also replaced one of the easier to reach vacuum lines. I also added some Chevron Techron to try and help clean the injectors as one post mentioned. The old air cleaner appeared to have NOT been installed very good and it appeared I might have been getting some blow by causing the lean condition but I installed the new one carefully ensuring a tight seal and I still got the P1128 code. I then decided to try the O2 sensor next. (This was also a bear to get out. I had a 22MM open end wrench that fit the O2 sensor perfect but the space was so cramped I couldn't get any kind of push or pull to break it loose. I decided to spray some WD-40 on it and then lightly tapped on it with a hammer to try and loosen it up. Still couldn't get it off. Checked all over for a 22MM crowsfoot and couldn't find one. Settled on a 7/8" crowsfoot on closeout at Sears.com - Got home and set the crowsfoot up with a long extension and got ready to crank on it and on the first pull it came undone so easy I about fell down. Guess the WD-40 and letting it sit overnight helped loosen it up...but it didn't fix the problem as the P1128 code came back - usually always between 27 & 45 miles of driving after clearing the code.) I then decided to replace all of the small vacuum lines as the other one I had replaced broke apart when trying to take it off (It was very rotten). I don't know what the secret is to getting the OEM clamps to release on these small vacuum lines but most of them are a bear to get off. I put my vacuum lines back on with a good quality zip tie. The vacuum line that is the longest and runs from the drivers side over to the passengers side and connects below the airbox into the Diverter or Blow By valve gave me problems. It seems to be easier to work on by getting under the car. Get the car up in the air as if you were changing the oil (remove the plastic belly pan) and trace the vacuum hose down under the airbox to the Diverter Valve. The clamp holding the hose to the diverter valve didn't have a way to release it so I started prying with a screwdriver and broke the stem/nipple off the valve that the hose plugs onto. That was okay as I found out the stock valve is weak and the new part number ends with a "N" or in some cases if you get an '05 model or newer it ends with a "P". The ones with a "N" are around $38 and the ones with a "P" are about $47. I ended up with a "P" inside of a "N" box so I paid $38 and got the newer upgraded "P" Diverter Valve. Got the codes cleared and am still pulling the P1128 code. Basically I figured I would try the MAF and if that didn't fix it I was going to take it into the dealership as I had scheduled an appointment a week earlier but they couldn't get me right in :~). Anyway I installed the MAF into the top of the Airbox lid. It was a bear to get the lid high enough to work comfortably. After removing a few of the hoses and loosening up some of the wires, I was able to get it high enough to get the MAF replaced. Then on reinstalling the airbox lid, I noticed a small filter that is gray/white on one side and black on the other near the back of the airbox and it was in horrible condition. All deteriorated looking and I remember seeing a post somewhere about that. So on my way to get my codes cleared I went back to the dealership and replaced that valve. It has an arrow that points and word that reads "Motor" on it. Anyway I replaced this little valve ($18) and then had the codes cleared and my Check Engine Light (CEL) hasn't come back on since (700 miles later). I took it back to the place that wouldn't pass me before on my State Emissions test and it passed this time. Hope this can help someone else. It didn't appear my vacuum hoses were causing any of my problems but as fragile as they all were if any of you Audi owners haven't ever replaced them even though they are tough to get to, I would do that to save a problem down the road if your car is 5 years or older. I will start with the MAF first if this happens again. I also tried to get my car Vagged and the three people in my area didn't have a laptop in working condition to help me out. - Total cost of Audi parts purchased from local dealer $450.00 (O2 sensor, MAF sensor, Diverter Valve, white/black valve, and 3 meters of vacuum line @ $9.00 per meter) - Good luck - Scott