Short story,
Dads fox mustang developed a nasty vibration about 2 years ago. due to outside issues the car sat until about 2 weeks ago. We seperted the converter from the motor, vibration was still there, so we tried a new balancer, no luck either. Pulled the motor apart to find that a side wall to one of the pistons had broke off, but was still hanging on for the ride (was still going up and down with the rest of the piston). Got a new piston and the rest were all pulled and checked for damage. Got the motor back together yesterday and all though not as bad, the vibration is still there at about 3000 rpm, but subsides at idle and when revved about 3k.
Any ideas?