Engine Intermittently runs rough?

My car's engine started running rough while at a stop light. After I parked for an hour and restarted the car, it ran fine going home. The next day the car ran fine, but two days later it had the same issue. I changed the plugs and coils, and the car ran great for 2 days. On the 3rd day, I started the car, and it ran rough even after stops. Today, I started up and it ran fine and gradually deteriorated.
Here are the tests I attempted: The ECU had code 55, which is 'no codes'. I unplugged the MAFS and the engine stopped, which I think means it's okay. I looked at the throttle body and it is dirty, especially since the PVC occasionally throws some oil down the line. I have no idea if the EGR is working. The gas cap usually has back pressure and I burp it. One time I drove without a gas cap. Fuel filter was new about 2,000 miles ago. My previous mechanic is 'unavailable' to work on this problem. Where do I go from here?