my psi should be holding at 21...while im doing highway pulls i can get it to about 19ish which it will either hold or dip depending on its mood..i did some vag com logs and my boost and actual were the same...i did the n249 mod and thats when this all starting happening...i put the valve back to factory and its still doing this...i did throw an intermittent o2 sensor code, no cel's...someone please help me fix this

things i think it might be....
1. maf
2. callapsing tip
3. the o2