Q: My car has a throttle position sensor issue so I replaced the entire throttle body and the light came back on. Any ideas?

There is a relearn/calibration procedure that is typically performed whenever the throttle position sensor is replaced. If that procedure was not performed, it might be relevant in your case. The code (P0121) that you are referring to implicates not just the throttle position sensor but the entire circuit. That means the wiring and connections need to be confirmed and then the actual output of the sensor has to be read and graphed on a scan tool. Once all that is done, the underlying fault should come into view. The fan noise might be relevant (the fan noise may indeed be the cooling fans), that is if the noise and the warning light are coincident that suggests some sort of electrical problem like maybe a voltage drop (caused by the fans starting) affecting the TPS circuit. A scan tool can detect that. Indeed a scan tool can command the fans on and then you can see if that causes a malfunction elsewhere. The coolant leak is a comparatively simple issue. My recommendation is that you request a check engine light diagnostic and a certified Mechanic, dispatched by YourMechanic will get the trouble code resolved. At the same time, the mechanic can inform you as to what is required to resolve the coolant leak. If you have further questions or concerns, do not hesitate to re-contact YourMechanic because we want you to make the most of your repair dollars and help you to get the best possible results.