Wondering what's wrong with this Escort.

Ok, so I bought this Escort ('98 Automatic 2.0, 90,000 miles) and it had been running fine through winter although occasionally it had trouble starting. One day about a year after I got it I was driving up a hill and I heard this loud ping coming from below me. I took it in and they told me my fuel pressure was 5% under and that fuel was leaking back into the tank. They said I should have my fuel pump replaced but that it would cost $650 (I think they were trying to hose me). Instead, I drove it home and had my neighbor put it in. Turns out, it wasn't the problem! By this time acceleration had greatly diminished. Idling was rough (seemed to be missing) and sometimes when I would stop it would stall and need to be restarted. Code P1131 came on (H2O sensor running rich or something). We cleared the code to see if it would come back on (is that what you do?) But it hasn't yet. My neighbor suspected the catalytic converter because air was only puffing out of my exhaust. He drilled a hole in it and it seemed to help. Now this is silly and also illegal, but he started chipping out the rhodium to make a hole so it could breathe. Sadly, this only wasted a good converter. I already changed spark plugs and filters but the problem continues. I really just don't want to take it to a shop and get taxed, you know? Any help would be excellent! Thank you Bob or Ken! Crying or Very sad