I bought a 2001 Hyundai XG300 with a blown motor. Replaced the motor with a good used one which runs good and have had all kinds of problems with check engine light and several codes. Currently the car has P0115 (engine coolant temperature circuit) and P0141 02 (heater circuit bank 1 sensor 2). Also the air bag light came on.

RPMs go up and down slightly at idle. Transmission slightly jerky from a stop at idle in drive and also reverse. I think the idle fluctuation is influencing this.

Any Hyundai experts out there that can tell me how to solve the problems on this car?