Question about my URS4
 

So I had a question about my URS4, so I will try to give as much information about the car as possible, so as to help with possible diagnosis. Car is a 1993 Audi S4, has approx. 250,000kms on it, runs great drives great, car was original owner when I purchased it last year. Car was also completely stock when I purchased it.

I immediately noticed that sometimes during boost, or heavy acceleration, it would bog or sputter, I investigated and found the common problem of the POS units failing. Now in the meantime I have added 2.5" straight exhaust to the car, and an intake. I'm from canada and it gets quite cold, and I noticed the sputtering problem getting worse, and the stumbles were quite heavy, and could happen at any time. I replaced the POS units with the Apikol 1.8 conversion kit, and immediately noticed an ENORMOUS difference.

However, I still get the occasional stutter, and these sputters are incredibly small like split second, and they never seem to occur during heavy throttle or boost, 9 times out of 10 they happen either under normal acceleration, or just randomly as I am driving along.

I've also replaced the fuel filter, in the car and oil is changed every 3k. Just wondering if maybe it has something to do with the cold? Or what it could be, any help as always is much appreciated.