for what it's worth, the e.c.u. doesn't rely on either the o2 sensor or the e.g.r. system as a part of its cold start or cold driveability strategies.
Originally Posted by Snapperhead
one of the main things it looks for before going into closed loop is for the o2 sensor to be at temp so it can rely on output from it (which is non-existent when it's cold, also the reason why they went to heated o2 sensors vs. the original 2-wire non-heated design).
the e.g.r. system is used to lower the temperature of combustion, which aids in closed loop emissions. it isn't active during the cold start/cold driveability as the desire is to bring the engine and exhaust (read: o2 sensor(s) and convertor(s)) up to temperature as quickly as possible.
I designed, built, and programmed my own EFI system, so take what I know with a grain of salt.
Idling uses very little fuel if idling while the engine is fully warmed up. If idling cold, then much more fuel is being burned due to warmup enrichment and the fast idle valve operating. Take into consideration that at idle, you are running at 'about' 13.5:1 (not stoich like most believe). Keep in mind, that ratio isn't part for part volume-wise, that's weight wise. 13.5 pounds of AIR for every pound (or 1/6th gallon) of fuel burned. Not much.
Normally modern EFI engines are open loop at idle and wide open throttle, and closed loop at light cruise conditions. I know of no system that is closed loop 100% of the time. It would be a recipie for disaster.
To me, it's a non-issue if the vehicle is fully warmed up. I don't however let the van warmup in the driveway in the morning. Just get in and go. It will warm up faster and use less fuel. Both saving you money in the long run.
As far as sitting at a light, if you're in "Drive", then there is more load on the engine to maintain an idle than if the engine is in neutral. Think about it.
There area lot of things that effect gas mileage. The pencil pushers that want to 'fine' an employee for 'idling' need to get away from the desk and get some first hand experience under thier belts. Or let us go watch them work for a day and start fining them each time they log onto Yahoo, Craigslist, or Ebay during thier normal work hours. That could level the playing field. :P