[ltd]

XR6 MArtin is Spot on, but added to his point is that the two pistons sliding up and down in the cylinder are actually reciprocating masses, meaning that they have to not only overcome their weight, but the added pressure of compressing the air/fuel mix. If you apply Newtons first law of physics which is that force equals mass times acceleration or F=MA, then you find that say a 2kg piston at idle of about 750rpm in a cylinder which travels 10cm on the upstroke and 10cm on the downstroke; it works out that the piston is moving at 2.5m/s.

Now, apply this to the weight of 2kg which equals 20 newtons and you have 50 Newtons of force required to overcome just the weight of the reciprocating mass. Now, with 2 cylinders firing simultaneously you'd require 100N of force, and this is not taking into consideration the load from compression and the friction against the cylinder.

Now, lets say that X amount of fuel is sufficient to get one piston (50 Newtons) to do its thing. Halving that will produce 0.5X which in a perfect world will give you 1.25m/s of one piston; so half idle of 375rpm. Now, double the weight to 100 Newtons as you want two cylinders to fire simultaneously, so you have 0.25X as the fuel component trying to overcome the 100N of force required to move the reciprocating mass meaning that it will travel at 0.625m/s or idle at 187.5rpm.
As anyone will tell you, it would not be possible to idle any reciprocating engine small enough to fit into a car, especially considering the weakness of the power stroke. Further, that weak power stroke would not be able to overcome the other forces applied to the piston such as friction, compression, thermal efficiency and a host of other issues. Basically, what these guys are proposing is bogus.

As for leaning of fuel burn; do you may remember a case about 12 years ago of a commuter airplane crash in Whyalla SA?
In this case it was found that as pilots have leaning procedures of large capacity engines, the junior pilot in this case overleaned the two turbo charged 6 cylinder AVCO Lycoming engines to the point that the cylinders got so hot, he burnt holes in 3 of the pistons, burnt valves and melted the electrodes off the spark plugs (2 in each cylinder). Subsequently, both engines failed and he crashed killing all those aboard. No, I refer to my earlier post about EXTENZE as to the veracity of the claim made by an amateur website at best.