combatkev82

Afternoon all ,
Ive got a wrx bug eye 2001 , just after some advice with fixing my poorly impreza . any advice an help more than welcome .
p0102 maf sensor - is this just a simple replace or could it be more
p0113 ICT sensor - no idea what this is
p0546 exhaust gas temp sensor circit - no idea again
and p0420 catalyst efficiency below threshold - is this because of decat and is it a replace cat or remap job .
like i said before in many post iam new'ish to the impreza engine so any advice would be more than great ,
thanks
Kev