Mazda Repair: 1994 626, 188,000 miles, compression check, older cars

Question
runs real rough and vibrates heavy when you come to a stop my mechanic says its not the plugs or pug wires. it vibrates when you press on the gas if you are travelling at 60 miles it runs smooth if you slow down to 50 that's when it will vibrate if you increase you speed it will smooth out.

Answer
If the plugs and wires have been ruled out then the coil is next to be checked then the cam/crank pick up sensor which feed it a signal.  The problem you describe sounds like ignition break down at some point.  If you have been driving it for some period the condition of the spark plug tips will give you and indication as to which cylinder(s) is at fault.

Fuel injection on each cylinder, pulse at the injectors.

Beyond that a compression check on each cylinder to determine excessive wear or possible a burned/cracked exhaust valve,  Common in older cars especially if you can detect an exhaust leak near the manifold..