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citreon synergie 2.0 petrol and lpg - Engine running problems on lpg and petrol - cyberfruits
The car when cold will idle, however if you drive it and say come to a junction or roundabout and wish to decelerate in a normal but rapid (and not timid driver) manner, the car will stall will stall when you come to a stop or when you engage the clutch and are idling/coasting (even before you stop at the junction.)
When it does not stall or when you idle normally the engine will race ( instead of idling of at say 1000rpm it will go up to 1300rpm and then as low as 800rpm) it will do this whether you are on petrol or gas.
When the engine has reached its normal operating temperature for this time of year (according to the temperature gauge – about 80-90 degrees Celsius) all the problems will go away on both petrol and gas and no longer stall at junctions or race.

The car had a full service including spark plugs, HT leads and brand new coil pack

Another piece of info which may be relevant:

The yellow petrol low warning light stays on far too long before the needle moves up and over when there is enough petrol in the car – when you start the engine initially. At times this light may come on for apparently no reason (when in gas mode and therefore not using petrol) in the middle of a journey; it will then go out even though you have not put any petrol in.