My 93 honda civic si won't go over 3500 rpm in any of the 5 gears. My check engine light is on and it just started doing this. I replaced the dictributor cap and fuel filter. I 've heard it could be everything from the fuel pump, speed sensor, the ecu, valve timing control or many other things. Do you have any suggestions?

Find out what code was thrown:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-6.html#post832012

It could easily be a bad Ignition Control Module (ICM) or coil, which I would replace anyhow on such an old Civic:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-4.html#post265896