I recently found that my 2001 4.0 warms up much faster and puts out good heat when I hold it to 2000 - 2200 RPM for about 6 to 7 minutes at a cold start. Question: how much extra gas would it be using then?
I feel it is best to warm petroleum fluids slowly . When the engine runs, power steering, and Automatic transmission fluid are also warmed by internal friction . After a minute or two, your ready to roll . Not to argue, but your procedure isn't best for the car . PS Have you ever seen a warmer car ? Takes a bit to warm up, interior stays warm all day .