Idle vibration

2000 Jeep Cherokee Sport 4WD 4.0L. I've been having this problem recently where upon starting the car I'm getting very bad vibrations. The best analogy I can make is it feels like driving over the lane guides on the highway, (the ones cut into the road). It happens after it's started and usually when idol; like at a bank or fastfood drivethru. It has happened once or twice going fast but is more frequent in idol situations. The only thing I did associate when it was happening is that when it's cold out it doesn't seem to happen at all; only when it's moderately warm to hot weather.

Thanks in advance.

Marc

Ther are a couple of tsbs out for what you describe.One is for putting a sleeve on the number 3 injector to keep it cool.Basically what can happen is if you had the recall for the exhaust manifold heat shield done(looks like a piece of aluminum foil on top of the intake manifold)all the heat that comes up from the exhaust manifold pretty much is directed right to the number 3 injector and what they say happens is the fuel is being vaporized in the injector.this causes a rough idle and / or misfire.This pretty much happens only when its hot out.there's also a tsb to reprogram the pcm.