The AOS has different symptoms will it begins to fail. Mine made a loud squealing sound after it warmed up and only then. A Porsche mechanic told me the AOS was bad and the squeal was the result of air being sucked around the front crank seal. If yours was squeaking on start up, I would bet you have a different problem. Also, if it ran good and you replaced the AOS, I would look for a vacuum leak and yes, you should have replaced the J-tube. Last question...did you have smoke coming out of the tail pipe.
