[Focus-Ak]

So what you have in your example is a 4.8% improvement in MPG, and a 4.5% reduction in fuel consumption. Incremental changes add up, and an increment from a reduced idle seems worthwhile for those who pulse and glide on open roads, especially (from my experience) hilly ones.

On slow city streets I think I probably glide over half the time, and then there is time idling at stop signs and (sometimes engine off) traffic lights. So there is a lot of opportunity there to both save gas and improve mpg (or l/100-km) as well.

------ Later edit, Jan. 28

I have calculated my average idle time from a datalog. It is from a 13 minute trip at mostly 40-50 MPH (some 30-35), no stops, with 23 pulse/glide cycles, starting and ending at the same place.

I used power 26% of the time (average 9 seconds, range 2 to 29 seconds).

Idle RPM coast time was 56% (average 19.3 seconds, range 4 to 60 seconds). Low idle differed on the glides, 600 to 750 RPM, usually about 650 (Focuses have a mind of their own on this).

The remainder was the RPM decline with zero throttle (i.e. dash pot effect) which was 12% of the time (avg. 4.1 seconds, range 3 to 5 seconds). Notably, these drops are much faster than before tinkering when my "low" idle was 1500 to 1600 RPM (idle drop to get there, 7 to 8 seconds). The Focus is notorious for having a high idle (many complaints on other forums).

So, I am saving in two ways; lower idle and faster drop to idle, the latter being important to make the most out of P&G driving.

Lowering my idle as above has made a repeatable difference of about 38 vs 41 MPG on this same route, measured on an UltraGauge, which is nearly an 8% gain.