Rise Idle speed to max rpm allowable - MPG lowering? significantly?

I have a bad vibration at idle which disappears quickly if I rev the engine just a bit so I am thinking of rising the idle rpm upto the max available rpm...
Since the higher rpm will be only at idle I expect no significant MPG lowering...
What can you tell me about this? What do you think?

I think you may want to have your injectors looked at, rather than raising your idle.