will not accelerate, dies

I bought a 98 Mystique recently which only has 82,000 real miles on it. When I got the car it had an issue with when yiu gave it gas to go it wouold hesitate stutter and then go. I replaced the Mass air transfer unit, the TPS, and the IACV. Now when I start it and lwt it idle for sometime I can finally give it gas without it dying, but after I drive it ten minutes it will not let me give it any gas without dying and will only idle. I had a ragged connector I put back together and have ordered a new one and I hope that will help, but I am not too hopeful it will. The engine runs fine and doesn't have any obvious mechanical problems, just the fuel feed it seems. I got codes Po171 which is the o2 sensor on the upstream making it run lean, and I got a p1121 which says the MAT and the TPS are not working together properly? They are both new so I hope that is the TPS connector doing that on the TPS, a p1504 which I believe was an ssue with the air intake circuit malfunction? where is the air intake circuit located? I don't know that one? So the codes other than the air intake circuit, and the o2 sensor are naming parts I have replaced new. The o2 sensor looks new, but I will replace and I don't have a clue where to look for the "air intake circuit" any of this ring anybodys bell.??