After a month of checking things for the problem of chugging from 1500 to 2000 RPM, (I put in new plugs, new wires,checked egr, vaccum leaks, changed fuel filter, looked for induction leaks, checking connections, cleaning throttle body, checked air filter, checked PCV.) I was poking around in the engine bay and noticed that the weap hole was leaking and it could be leaking on the opti? It this possible and could it cause the miss described above?
I am thinking of new water pump and opti. Please help/comment thanks. Robert

 

I had the same problem, the one thing which you havent checked could very well be the problem!! MAP SENSOR