rifkin

Okay I have a 2003 Mustang Mach 1. I am posting here because I am guessing the general forum has more views than the mach1 specific does.

Here is the story:

Recently I installed a o/r mid pipe. Right now I am running stock manifolds and the stock catback (soon to change), and it also has a k&n intake and filter. When I installed the H pipe, my upstream o2 sensors would not come out. so I installed it and ran it for a few days without upstream o2 sensors. A code was thrown and I didnt check it out. I also couldn't tighten down the passenger side pipe to the manifold all the way so there was a leak. I installed the new o2 sensors and the code went away, but I still had a leak. A few days later a code popped up again and I checked it. It said bank 1 was running lean and I am 99% sure bank 1 is the passenger side. So I attributed this to the leak. I took my car to a mechanic and had him fix the leak which involved him drilling out the studs on the manifold and bolting it down and what not. 145 euros later and the exhaust leak is fixed. Now my car is sealed up tight. The way it stands right now is, 2 new upstream o2 sensors, 2 downstreams with 37k miles on them. no cats, no exhaust leak. The code still exists. What should I do?