There was an article in The Age's Good Weekend, about 12 months ago, by Karl Kruszelnicki. Some of what it says:
- Engines run best at their design temp. Idling is not the best or quickest way to warm up an engine. GENTLE driving is.
- When idling, the fuel is not completely burnt. Unburnt fuel condenses on the cylinder walls, washing the oil off the cylinder walls and also thinning the oil.
- Idling drops spark plug temps, leading to dirty plugs, causing poor fuel economy.
- Idling prevents the catalytic converter reaching its design temp (400 -800C).
- Even in Canada, at -20C, it is recommended no more than 15-30 sec before driving from cold start. So even less is desirable in warm Oz.
Canada's Office of Energy Efficiency calculated that 5 minutes less idling each day would save $646 MILLION in fuel costs and and 1.6 million Tonnes greenhouse gases per year, in Canada alone.