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.

 

from what i can find check your fuel pressure check your residual fuel pressure your system might be losing fuel pressure after you cut the car off. there should always be some pressure in the system

at idle pressure should be 50 psi

after you cut off engine wait 10 mins pressure should be above 36 psi if not you have a leak or faulty check valve in fuel tank

 

i had the same code show up on my 2.8q when my dad put in 89 octane gas and didnt tell me. it also misfired. i simply drained the fuel and put in 100 octane znd added a bottle of fuel stableizer and cleared the code, let it run for about 30-60 minutes. everythings seems to be running fine after 4 months.

 

Could be a vacuum leak.

 

intake/exhaust leak, AIR ststem, hose leak