presumably the ECU lifts the idle speed back up. If you gentle the clutch up (with no use of the throttle), and ease the revs downward, the stall doesn't happen. The kerthuddd-stall happens (I think) only when the revs dip suddenly below idling.
Then again, it's possible that fuelling at idle is so lean, even gentle torque just isn't available. On Citroens, taking a little power at sub-idle simply results in slightly increased fuelling to prevent a stall (unless you overdo it!). Why the ECU couldn't have been programmed to lift the revs back up to idle is puzzling. This causes the engine to immediately stall whilst still in gear, and the shock to the transmission, engine and drive-train is quite alarming: like its being stopped with a sledgehammer. Interestingly, what doesn't help on the 4.2 D4D is the designed-in function whereby fuel supply to the engine is suddenly cut if you try to drive at below or just below idle speed (eg when executing a three-point turn, or letting in the clutch just a little without opening the throttle). DMF-thinking must be tied in with all this. are also concerned to minimise engine low-speed vibration and judder (for whatever reason), and a smooth start must help in this request. and will do almost anything to minimise these emissions and fuel consumption - often to the point of absurdity. bad for 'image', and don't help in the testing leagues. Toyota (and others) nowadays are very focussed on minimal emissions (smoking) on start-up. I've never known this on non-common rail diesels (eg older Citroen-Peugeot) which always fire up immediately when warm, BUT can be ragged to start when cold IF you don't let the glow-plugs do their stuff for a few seconds.
Why the delay in starting? Could be as Don suggests (pressure build-up), which would avoid a possible ragged or lumpy start-up.
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