Injectors and glow plugs are best removed on a warm engine - never stone cold.

Glow plugs are used for more than just starting - they are turned on at other times too (as part of the emissions system). On a car with 100,000miles or more, I'd replace them all and the glow plug controller if the engine is the M57TU.

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Wayne
2005 BMW X5 3.0d (b 02/05)
2001 BMW F650GS Dakar (b 06/01)