Is it true that the tune "Wears off?"

Not saying the car starts to run worse or anything... I mean the ACTUAL TUNE itself changes after a period of time?

 

Are you asking if the programming in the PCM changes? Or are you asking if what would be an optimal tuning for the engine changes as it wears?

 

The parameters of the tune never change until someone changes them. Things like short and long term adjustments to fuel delivery are constantly changing, but only to meet the parameters set in the tune.

 

No.

The 'tune' will command a control module to operate the engine at a set of desired parameters.

For example: 13.5:1 AFR @ 25 deg timing at 101 kPa of MAP or xxx flow on a MAF. This will never change by itself.

The controller will use it's sensors to try to meet those commanded values under different operating conditions. O2 correction, temperature correction, pressure correction... etc will cause fueling and ignition to differ in order to try to reach the commanded operating point.

Over time, things will happen... an O2 sensor can get old, plugs get dirty, fuel filter or injectors get clogged... These will cause the controller to do different things to still try and reach the commanded operating point.

Most of the time, the amount of correction that can be applied by the controller is limited. When the commanded operating point values can no longer be reached, different things can happen. A stock PCM would throw up an error code. A stand alone controller may or may not be able to tell you that something is wrong, depending on how it is designed.