I'll settle for educated guesses at this point...
Ok, I will try to give you a bit of background without boring you to death (key word being try)...
I currently have 2008 A3 FSI with about 120,000km on the car.
The car is stage 2+ I have a APR HPFP, APR 3" downpipe with Sport catback and APR stage 2+ software. Untill last year I still had a stock intake with just the Carbonio air box and the car ran fine. Last year I decided to upgrade to a Neuspeed P-flo intake.
Soon as the intake went on, car would go into limp mode, loose power and no codes would show up. The car wouldn't show any fault codes but if I would clear the codes the car would run fine for a while, sometimes feeling even more powerful than before. APR made an educated guess that the most likely culprit was fuel trims maxing out but didn't have a solution aside from buying one of their VW Racing intakes and trying that.
Stock intake went back on and the car ran fine. But I tried getting the VWRacing intake and the Forge Wintake for many months without success. Eventually ending up with a Forge Twintake.
Installed it last night, car ran fine. Drove a bit today, car ran fine... went to my mechanic to replace the spark plugs this afternoon. My mechanic set them at a 7mm (0.0275) gap old plugs had about 60,000km on them and were totally toast but the gap on them had been what came out of the box which was about 9mm (0.035). When I went for a test drive the car felt down on power though.
Took it back, checked for codes and nothing. Reset codes and the car ran like it's supposed to again. Looked like the mysterious limp mode came back again. Took the car for another test drive and the car started having serious backfire in 1st and 2nd gears and felt like it was over boosting a bit.
Tried resetting the APR program from 93 to 91 and the car seemed to go back to normal, even ran fine when back into 93 octane program.
But since than it has gone limp 3-4 times, the idle can't seem to settle down sometimes and twice the idle would get stuck at 2500rpm and only very slowly come back down to normal.
Once again, no codes show on VCDS but when I reset them the car goes back to normal again for a while.
Can anyone please help me and maybe shed some light on what the hell is going on?
Thanks in advance for any useful feedback.