You might want to look for a dangling vacuum line or a hole in the air intake past the MAF sensor. Any fuel injected engine operates as a closed system with carefully metered air and fuel. Introducing excess air confuses the ECM. All the ECM can do is look at the air flow, look at the engine temp and adjust the gas injection rate. Air introduced past the MAF will give you poor combustion and a bad signal from the O2 sensor which will send the ECM hunting for the right mix. Any air leak would have the same effect so check the gasket on the intake manifold and the valve cover too.