1993 Honda Civic Car revs up and down whenever I turn it on

Engine problem
1993 Honda Civic 4 cyl Wheel Drive Type unknown Manual 216000 miles

I had just recently replaced my thermostat only to find that there wasn't even a thermostat, only an old gasket for a thermostat. After starting my car, the car continued to rev continuously, from about 1500-2500RPMs, and soon after placing more water into the radiator, the car wouldnt die, but the revving still continued. This has been a problem since I have purchased my car back in may, and I have really had it. Tonight when I went to the gym the car revved up from 1500->3000 and stayed there for a while. I waited 5 minutes, and it still continued so I drove to the gym which is about 1 mile away from my house. The whole way there while not in gear the car persisted revving. And while in gear and not having any pressure on the accelerator, my car would drive on as if there was pressure. About half-way home from the gym the car stopped revving. What I dont understand is that I replaced the thermostat and now it seems to be worse. Is there something wrong with my choke or heater? Because the heater doesnt work as well. Any help will be appreciated.