It took several seconds to shut down because it had to use up all the residual fuel that was in the filters, injection pump and lines. If it was running away on the oil in the engine, it would keep running until it used up all the engine oil or catastrophically failed.......

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2012 Mercedes ML350 Bluetec 102K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 238K (mine)
1998 Volvo S70 T5 Turbo 211K (kids)
1994 Ford F150 4WD 246K (firewood hauler)
1983 Mercedes 300D 384K (diesel commuter)