My furnace is cycling on and off, no matter what the thermostat is set for

My furnace just keeps cycling on and off, about 90 seconds at a time no matter what the thermostat is set for. I can turn the thermostat all the way up to 90 degrees and it will turn off after only 90 seconds or so. I can turn the thermostat all the way down to 60 degrees and it still turns on. I can turn the thermostat off and take it off the wall completely and it still turns on. I can jump the red and white wires and it still will not turn on until the 90 second cycle is up and even with the red and white wires not connected to anything, it still cycles at 90 second intervals. I tried turning off the switch and turning it back on, but that didn't help.