Actually, they use less fuel when turned offIdling for more than about 30s uses more fuel than switching off/on. 60s is the break-even point if you take into account battery & starter motor wear.
Unless you've been thrashing the engine beforehand, it is not necessary to idle-down the turbo. The Skodas are fitted with a post-shutdown water pump that circulates water through the cooling circuit of the turbo & a similar pump for the oil supply. So unless you've been doing hotlaps of the local area, idle-down is redundant. Turbo-Timers are very 1990s.
Prolonged idling in any turbo-diesel is also an outdated idea. All it does is use fuel, pollute the air & wear out the engine. It causes a thing called diesel plugging which is a build-up of carbon around the rings & other components & also wetstacking (buildup of liquid soot in the exhaust circuit).
Basically, a diesel is designed to operate under load. Idle doesn't load them enough. If you need to sit for prolonged periods then you need to bring the RPM up to 1200 to load the rings, increase EGTs, increase fuel burn efficiency & reduce water vapour.
My info is based on what my engine vendors (Detroit Diesel/MTU) were telling me when I was buying stationary engines off them between 2002-2007. We were having issues with the operators wanting to idle the engines for excessive periods (causing plugging & wetstacking) & the vendors wanted to put in an idle routine in the ECU that would punt the engines to 1200 if they idled for more than 5 minutes.
Sorry for the lecture but there are a lot of outdated practices out there in diesel-land.
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