Loosing power when Engine warms up.
 

Hey. I have an s14 95'. I noticed that my car gets sluggish after I drive it hard for a while. I had an engine check light, checked it and it gave me code 55 which means everything is ok. I haven't had anymore since then, it turned on after I hit about 64,500 miles. My engine feels pretty strong at first, but after some hard driving it feels like it's lost power, revs up slower, etc...even my exhaust sound changes, it becomes an annoying farty mid-rangy noise. I'm about to replace the o2 sensors and add headers. I already replaced the fuel filter, spark plugs, cables etc... can anyone help? thx :(

clean the mass air flow sensor, and it could have dirty injectors. could be the fuel pump tryin to take a dump

I'll try to clean the sensor you specified, i'll check the injectors too. My car idles fine though, it idles at 750 rpm with no shaking or anything, could it still be caused by the fuel pump?

It could be, but im not 100% sure. You should also check your vacuum lines too. But it might just be your o2 sensor. Defiantely clean your mass air flow sensor. that is usually the first source of the probs.