engine cutting out when coming down gears to stop

i have had a problem for a while which is getting worse, when choke comes off erratic idling , also when i am coming down gears to stop the rev counter goes up and down and when i come to a stop the engine cuts out, i have checked plugs and coils etc, also for a vacuum leak at throttle body, when i got the car it was intermittent but has got worse, the only thing i can think of is the timing, as the belt was changed at 71000 odd miles now 88000, the only thing that was not changed was the dephaser which is noisy at idling speed, could it be that or the timing was not done correctly. Thanks

i forgot to say Laguna 1.8 53 reg

engine cutting out when coming down gears to stop