P0506 Mitsubishi - Endeavor 2006 Timing Belt/Sensor Issue AND rattling underneath the vehicle

Question

The "service engine soon" light came on in my 2006 Mitsubishi Endeavor about a month ago. When I brought it in to the nearest Auto Zone for a diagnostics test, this is the code I received: P0506 Mitsubishi - Idle Control System RPM Lower Than Expected. In the past, when I the light came on with this code, I would simply replace the air filter (which was dirty) and the light would turn off. This time, as in the past, the light turned off after I replaced the air filter. However, about a week later, the light came on again, so I returned to Auto Zone and received the same P0506 Low Idle code. The night before my scheduled appointment with a Mitsubishi dealership, the light turned off and stayed off. I still went to the appointment due to a rattling noise underneath the vehicle. When the maintenance team examined my Endeavor, they said the rattling was more than likely a timing belt sensor issue and that this was more than likely tripping the "service engine soon" light.

Could a timing belt sensor be cause the P0506 code?

Also, about 4 months ago the same dealership removed (not replaced) the heat shield when I initially brought in for rattling. Could the removal of the heat shield have anything do with the timing belt not working properly, causing continuing rattling as suggested by the maintenance team?