Why Don't UFOs Stall Airplane Engines?
Greg assumes for sake of argument that the force that repeatedly stalls cars must be electromagnetic -- but that's not necessarily the case. Marc Davenport, in "Visitors from Time," suggests that UFOs bend the spacetime in their immediate vicinity, thus accounting for all manner of strangeness ranging from "missing time" to perceived changes in color.
Davenport also argues that the kind of vehicle shut-downs immortalized in "Close Encounters" are inconsistent with EM effects, noting that a field powerful enough to disable a car engine would permanently cripple the afflicted car. Consequently, documented cases of car engines spontaneously starting up once the UFO has left the vicinity would seem to be due to some other phenomenon -- possibly in keeping with "anti-gravity."
The speculative upshot of Davenport's book is that UFOs could be literal time machines, perhaps from our own future.