I would go with the suggestion of cleaning the MAF sensor wire. If that doesn't work see if you can find somebody with the same car borrow there MAF for an hour and see if it fixes it then go buy a used one if it does. Your new air filter was probably a little to oily from the factory and got it dirty. You could go buy the K&N cleaning kit and clean the air filter then re oil it your self. There should be no need to reprogram your PCM other than what you did by resetting it. I wouldn't worry so much about it idling at 500. My wifes car has done that since I did the Mousing fix over a year ago with no ill effects. Your new pipe probably is doing the same thing the cap with the hole does by reducing the amount of air it can suck in through IAC. Good luck and don't throw your money away at the dealer.
