*****The throttle was real stiff and my dad just wants to change it out. We
have an A&P to do work on the plane (he does lots of comanches)for
flying time and he said its no problem to change it, it take about 2
hours*******

Buy what FAA approved authorization will the "mechanic?" use to change the
engine control system? He sounds like an idiot to me.

Is there a STC for this?

Are you planning to get a field approval for this unauthorized modification?

You can't just "willy nilly" change critical control systems on aircraft
certified in the "normal" category without FAA approval. I doubt if they
would give such approval without an STC.

If it is stiff when cold, why doesn't your "mechanic?" just fix it properly?

Karl