i face a proplem sometimes with the engine running idle ,sometimes i feel a strange shake like if only 3 cylinders are working ,i only feel it while stopping (not always) ,

and it is not continous......my engine is 1.6 mpi.

My Fiat did this and the answer was - stop using cheap fuel.

Yep - all three of our Skodas do this. It's the cheap Sainsbury's supermarket petrol we all use. 

ok thanks guys but that's the best you can get in egypt's petrol stations

Try STP fuel treatment or an octane booster.