My buddy said that the car was running too rich by the smell of the fumes. I was very excited thinking that I fixed all my problems by putting the stock air filter back in. This fixed the idle problem, but the last couple of weeks have shown that the fuel efficiency is actually pretty bad. While I still plan to do full diagnostics soon, is it safe to assume that this is due to the aftermarket fuel injectors? Can the injectors alone cause a rich condition?

I failed to mention that before switching the air filter back, I stopped at Autozone a couple of days ago. Couldn't clear the codes yet, but a new one popped up P1166.

Solid CEL is on now. Took a quarter of the tank to go 40 miles today.

Whether the EVAP solenoid/canister had anything to do with the CEL or not, replacing it with another used Bosch part did not change anything in terms of the idle, but it did get rid of CEL. I also learned the hard way what that broken 'Y' piece was. It was not a vacuum hose but rather a coolant supply pipe to the throttle body. Spilled some antifreeze.

My buddy let me borrow an Elm327 wifi reader. I no longer have misfires and now down to P1166, P0113, and P0102. I already ordered an EGR valve ($110). I am crossing my fingers and really hoping that it's just the valve and not the O2 sensor. Would anyone guess otherwise?

Thank you!