1999 Chevy Camaro help

I bought a 1999 Z28 and the problem is the car is running rich and making the service engine light come on, code p1153 (02 sensor) and so I noticed that there are performance injecters on the car that are putting out 43 lbs of fuel an hour, so I put stock injecters on that put 24 lb of fuel an hour and the car just wouldn't stay running, so I found a vacum leak and replaced the seals and that didn't fix it, so I put the performance ones back on and it's ok, but I still have the problem of it running rich, could it be a ecm problem, mabey because he programed the ecm and the ecm don't register to the stock injecters. Pls help