1991 Rolls Royce Silver Spirit

Engine Performance problem
1991 Rolls Royce Silver Spirit V8 Two Wheel Drive Automatic 18700 miles

My RR has recently been converted to LPG. After running for 1000 miles it backfired when transiting from petrol to LPG when warming up. Immediately the engine refused to idle and " died" at the point of idling. (On the LPG fuel it worked faultlessly). I have changed the plugs which were quite coked up with a tan coloured cement like substance and have found the idle control mechanism on the top of the engine but am unsure how to proceed with checking it.
Bill harding
August 16, 2010.

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