Once the car has warmed up the idle tends to be a
bit on the rough side as if the engine is stuttering and sometimes when the clutch is pushed in and held in the rpm's will jump up and then go
down low and it will
finally settle in between the high and low point.
If you plot them as a function of time, you find that one is a little bigger than Millikan's, and the next one's a little
bit bigger than that, and the next one's a little
bit bigger than that, until
finally they
settle down to a number which is higher.