My steering wheel vibrates when im on the free going around 68-70mph and i step on the gas. when i let go of the pedal the vibrating stops.

my front left tire had a flat and i plugged it this week.

whats wrong? what should i do.

please help...

 

Did they balance the tire when the patched it?

 

An unbalanced wheel usually shows up at lower speeds.
A bad CV axle could act like that.