06' Nissan altima please help need insight.

[timbmore]

P2A00 02sensor bank 1sensor 1,P0507 Idle air higher than expected. I have the 2.5s I just recently had a new head gasket put on. After that I found out my primary cat was clogged. I busted it out to confirm that was the issue with the lack of power. I had full power after that. I drove it for a week then i got crankshaft and camshaft codes. I changed them. Now i have the current codes. In subject box. It has been idling high. and fluctuating rpms since before the head gasket was changed. Now i'm back to having no power. I still have the same post-cat on. Not sure if that was the problem. So i took it off at the bottom of the exhaust manifold. left an inch gap between the pipes. went for a ride, I think it ran worse. Maybe because no back pressure. Now when the lack of power started my engine seemed to get a loud rattling in the top of the engine maybe in the valve cover. I have 188K on my engine. I think that my head gasket leak started small and it got so bad i had coolant smoking out my exhaust. I've read that the primary cat gets clogged and things can get sucked into the engine. I'm not sure if my engines just tore up inside. Would really appreciate any help or knowledge about my situation. So I don't waste anymore money on this engine.

Thanks for your time.

Tim.