my sons and my XJ if it sits and idles and gets to 210 degrees it will start idling really rough but once you start going down the road and catch cooler air and the temp starts to come down it will clear up qick and run fine. is this vapor locking? his is a 2001 and mine is a 98. any help would be appreciated. thanks

 

It for sure isn't vapor lock. Fuel injection doesn't vapor lock as the whole system is pressurized. As for what it is, hard to say. Many sensors could cause rough running when warm.

 

check to see if electric fan is kicking on, it sounds like its not and the engine is only getting cooled when driving.

 

210 is normal operating temp. If it goes up to 225 when sitting still, either the fan clutch is bad or the electric fan isn't coming on. When the temps get up to ~217, the e-fan will kick on and usually cool it back down to 210ish, and once you get moving, temps will drop to 200-210. The rough idling could be a number of things: how old the spark plugs are, spark plug gap, bad gas, etc.