Intermittently, after warm up, engine stalls when driving without any
hesitation, similar to turning off the ignition switch.  I have not
experienced this problem with the car left idling, but have occasionally
noticed erratic idle speed, which may or may not be related.  Engine can be
restarted after letting it sit with the ignition off for several minutes.
After restarting, the problem may reoccur after about 5-15 minutes or it may
not.  Problem first occurred after reinstalling engine with head replacement.
 Quite inconvenient if stalls in fast lane in bumper-to-bumper traffic.