handyandy

hi, i recently bought a 2001 mustang gt with around 90k miles, 5 speed manual, aftermarket intake and an aftermarket throttle body. I am have some gas mileage problems or what i think are problems when driving in the city, on the highway i get around 23-24 but in the city with modest driving i seem to be only getting around 8-9, no lie. Could the gas mileage problem be linked with the aftermarket componets? or do you think the oil on the air filter may have clogged the Mass air flow censor causing the ecu to add excess gas into the engine? I am not a very technical person so any imput would be great. Or maybe a chip would help? I really would like to get to the bottom of this so thank you for you imput and your time!