I started my 04 WRX this morning and it had a CEL. This was very curious, so I drove to Starbucks and had absolutely no power/no turbo spool. It was also making a pinging noise. (Read next sentence with an open mind) - My only mod, stupid as it is, is an AEM CAI. I know I am getting rid of it, by why would this cause this to happen. Oh yah...I then started the car up leaving the parking lot and of course still had a CEL, but had my turbo back like new. I don't need to hear my CAI caused this, but would appreciate an intelligent response as to why driving there it was like driving a Honda civic and on the way home I had my WRX back.
Thanks in response.

 

There's plenty of info on I-club and NASIOC regarding intakes and why most of them aren't a good idea on the WRX.
As for your CEL, you need to get the car scanned to find out what code(s) were set. In most states Autozone does free scans, but in CA they stopped that a while ago. They may allow you to borrow the scanner for a deposit and do it yourself. If that doesn't work out, try asking for help in your local forums and see if you can find someone with a scanner nearby. Once you know the exact code(s) in Pxxxx format, you can search for more information on how to deal with the problem in the tech forums.