CRX Check Engine Light & Unmanned Revving

I have a problem with my 2nd Generation Honda Civic CRX Si and just needed some answers. It has over 180k on the stock engine & well maintained. The problem started as such. One day, my car was revving itself beyond normal while running or at a stop and the check engine light came on until i restarted the second time. Prior to all this i changed the clutch which was slipping and it also did the strange revving right before that. The problem disappeared for a while (2 weeks) after i replaced the clutch and came back (possibly due to colder/wetter weather). I had some difficulty starting eventually as well and thought this was probably the problem, so i did a tune-up and replaced the distributer cap, rotor button, and plugs (& wires were fine). I also Cleaned the throttle body and lubed the butterfly area a little. Thermostat and radiator was also just changed. Air filter was fairly new and clean. It was starting fine and running fine for a couple of weeks. Last weekend the check engine light stays on even after restarting and i get the revving effect every now and then. This week the light is not on. When in Overdrive on the highway the car seems to be louder or possibly revving higher than normal as well.

Is it possibly an O2 sensor going bad? I can get a universal one from autozone (requires splicing my wires) or the whole plug set. This has never been replaced to my knowledge and it is $17 for a Bosch Universal one or an OE with plugs for $35 dollars.

Is it the Fuel pump? i'm hoping this isn't the case.

Thanks everyone!