mitchell1963

I have a 2003 GT Mustang and it runs sluggish but there are no check engine lights on.It has at least 140,000 miles on it and not sure if the fuel pump is working properly to supply enough fuel to the engine or if it could be a old fuel filter that needs changed.

WhiteFoxGT

could be anything, if you arent capable of determining where to start maybe you should drop it off to someone who can. might sound a bit blunt but asking here and waiting for us to speculate could cost you extra money on parts it may or may not need

GT Nate

might be a spot on the fuel rail you can attach a pressure gauge to...

99GTvert

When was the fuel filter changed last? How about the spark plugs? What maintenance was done to it recently?

Derf00

Blockage in the air intake

(just throwing it out there since we're spit balling here

99GTvert

Might even be a clogged catalytic converter.

pure_kaos

Could be a loose COP, IAC.. etc. etc. etc....

Z28KLR

Probably needs a new supercharger.

Z28KLR

For real though just do the regular maintenance items, any that have not been done somewhat recently or ever at all anyway.... Fuel filter, spark plugs, clean MAF. If you got an extra $10 sitting around that you're not doing anything with then dump a bottle of Techron in the gas.