1998 4cyl Camry

I have recently purchased a 1998 Toyota Camry 4 cyl. I had to replace the water pump as it was leaking coolant, I also changed the front and rear brakes and also the front rotors. As I was driving it after the brake change I noticed that I would seem to lose power, kind of like it wasn't getting any fuel or something. My rpms would go down, but most of the time would quickly rise again when I pushed on the gas. Any ideas on what my problem might be? Any help would be great!

See if you have any codes in your ECM.

I plugged it in and got three codes P0401: exhaust gas circulation flow excessive detected, P1133: air/fuel circuit response bank 1, sensor 1, and P0171: Air/fuel mixture system lean bank.. I obviously have a air/fuel problem but I am honestly not sure what any of these mean.

It may be that some of those codes are old. Reset the ECM (delete the codes) and drive it for a couple of days. Then check the codes again.