Volks,

The new engine is running OK, mostly.  But [there's always a but] sometime
when idling the engine has a hesitation, like it cuts out.  Usually it
catches itself in time and restarts but once it didn't.

And, [there's always an and] after it's warm and driving at part throttle
instead of accelerating and decelerating smoothly it acts as though there's
no flywheel.  It does the accelerate or decelerate but jerks at the
beginning.

Either or both of these sound familiar?

Mike