08 C30 Throttle Body
 

My car was making a slight whistle sound when idling after about a 4 mile trip, then the check engine light came on and it began to idle funny. I brought it to the mechanic and he said I needed a new throttle body. He replaced that and within 2 miles of driving my car home the check engine light came back on. The original code my car threw before getting it fixed was P0507 Idle Control System RPM - Higher Than Expected. The code it is now throwing since replacing the throttle body is P2187 System Too Lean at Idle DTC.

The mechanic said for me to bring it back so he can diagnosis the issue. Has anyone had this problem before? I feel like until the very moment my check engine light came on the first time my car was driving fine and had zero issues. Does this problem just suddenly happen?

This is a 2008 C30, 63k, manual, well taken care of and not beat on.