NO INITIAL POWER ON GAS ON PEUGEOT 206, 04 REG!?

When I put my foot on the gas, nothing happens until after 2-3 seconds, then the power goes to the engine, causing me to over-rev!! It's a nightmare on roundabouts, with no initial power!
The car cuts out when I move off after starting the car in the mornings. It has been like this for a couple of months.
It has been run on 2 diagnostics at gargages (one of which was at the peugeot garage) but nothing is showing up and the mechanics don't know what it is!!
The car is a 206, 1.4 engine, 04 reg!

HELP!