Engine shuts off while driving

The idle seems to be ok, the problem is the engine will shut off while I am travelling at interstate speeds (from 45 to 70 ), it turns off then slams on so hard it feels like the whole car jumps off the ground, I know that it is not actually jumping off of the ground, but it slams off and on so hard that I am a little worried about possible damage to the timing belt, I don't think it was designed for that kind of stress. It has just started occasionally turning off while I am at a traffic light, or slowing to stop. My neice had a similar problem with her car and it was something as simple as changing the spark plugs. The timing seems to be ok, all cylinders are firing, it seems like as soon as it warms up, it starts shutting off as I travel down the road.

as soon as my 99 jeep warms up it can shut off anytime. it wii always start up again. drives me crazy.

I had a tuneup done on my chrysler New Yorker, cleaning the throttle body was part of it, as well as replacing the plugs, plug wires, and coil. One of those items corrected the problem of my engine shutting off and then coming back to life at interstate speeds. Simple fix for a scary problem.