engine performance problem

I have 99 Chevy Malibu. My check engine light came on. The original codes were for a cylinder misfire and a small emissions leak. I replaced the injector for the cylinder that was misfiring as well as all the plugs and wires. After that I got a code that said my system was too lean. My car starting idling low and shaking the car. My dad has the same engine so I starting switching out parts to see if it help. I noticed the hose from PCV valve to the evap canister was connected so I attached the hose. I replaced the engine coolant temperature sensor at it made the car run a lot better it still isn't back to normal but it is not as bad. I got the codes cleared and the check engine light has come back on. Anyone have ideas on what it could be? I have until the end of the month to pass my emissions test and I want to get the car running right. Please help!
Other parts I replaced
orswapped out- MAP
sensor, MAF sensor, IAT valve, air filter PCV valve.