UK Car Repair: car wont go, air flow sensor, coil pack

Question
my renult espase keeps on going as if it is losing power or petrol  it keeps on going to stop and then going again

Answer
Sounds like a bad "Ignition Coil Pack", but that;s just a "likely" cause.
Have the diagnostics scanned at a garage to see if there are any error codes, Pretty sure this is an ignition problem but without much detail it is a poorly calculated guess.
A diagnostic scan should be around £20.
Ask around a few parts shops to find a decent price, get the actual error code - not the name of the fault... EG error code comes in the format  "P1111", and the fault would be "Misfire, Cylinder no 1", Get the error code for me and I'll diagnose it properly for you.

(it could be a bad fuel pump, it could be a bad air flow sensor... it could be any number of things, so the scan is essential, otherwise you're swapping parts blindly... that way you end up with a lot of used parts to put on ebay and a car that still doesn't run ;-)