012My 2001 Elantra started to shift erratically, with RPMs spiking very high. Check Engine light came on. At first I received 2 codes: P0121 and P0121 pending. I still don't know what the pending means. I replaced the Throttle Position Sensor and cleared the codes. Car ran fine for about 20 minutes and then RPMs started to go slightly too low or too high. I came to a stop light and put the car in park for a few seconds and the RPMS began bouncing between 1500 and 2500. The check engine light came back on and I got code P0303, misfire on cylinder 3. Can anybody tell me what's up?