Multiple random misfire

Good night,

A few night ago I drove my matrix through a heavy rain storm and the acceleration was sluggish. The check engine light came on so the following morning I scanned the codes and I got codes that indicated random multiple misfires on cylinder 1-4 and o2 censor running lean. I did research and it appeared that the some matrix had an issue with the air intake manifold seal. So I bought the seal from Toyota for the air intake manifold and throttle body and replaced both. I also replaced all 4 plugs. I reset the chk engine light and started the car and now I am only getting the misfire codes for cylinder 1-4 + multiple random misfires. Could you let me know what else I should change to remedy these misfires? Appreciate you