2000 Jetta VR6 Help!

Hello, I have a 2000 VW Jetta vr6 with 95000 and since day one it's been giving me all kinds of problems first thing I had to replace the MAF sensor and it was working fine a few days later the check engine light came back and I had the car scaned and the code was P0420 and it reads Emission Workshop the funny thing is that the light would clear and come back and now it's on for good. Recently I changed my spark plugs, Oil and Oil Filter and one day later the EPC and the ASR lights came along together and it reads Engine Workshop, I had the car scaned and I got the codes p1128, p1142 and p1101 I dont know what the problem is or were is coming from.I think there might be an air leak but im not sure were it's coming from the car runs good but sometimes it looses power on the engine and then power returns. If u can please help me find the problem on what's going on I would really appreciate it.

Best Reguards Moises Lara :|