2007 Renault Clio

Engine Performance problem
2007 Renault Clio 4 cyl Front Wheel Drive Manual 51000k miles

when I start driving my car (not just the mornings) all the time actually, when manovering there is no va va voom and its snatching really bad, its very dangerous espcially when im at a junction or roundabout infact, its really dangerous even when im on the motorway and I need to overtake. Its been in the renault garage twice now they have put new spark plugs on and changed 2 ht leads the first time, the second time they put a new timing belt on and had the head gasket off cause of an oil leak, its getting worse now and im just wondering if you have any ideas what the problem is so I can explain to the mechanic but its all supposed to computerised now and I carnt understand why the renault garage is not picking up on it. When I drive it away from the renault garage its fine but the next day its back to the way it was when I took it in. Now its not when the engine is cold cause I ive in tenerife and its not exactly freezing and also like I said its everytime I put the key in the ignition, plz hep so I can explain to the spainish mechanic what it is. Do you think I needs fuel system restorer in as I have been using 95 unleaded petrol not 98 but it does say I can use both,


cheers
diane.