In the box the previous guy mentioned there are 4 relays... a large square (Red) one, and 3 smaller black rectangular ones. The large red one is the Fast cooling fan, the three smaller ones are slow cooling fan, fuel pump, and IMMOBILISER!!. I have a 2000 clio172, had the same trouble, and it was the immobiliser relay. I changed all 3, but got them from RS components (www.rswww.com part number 535-2542 at £2.80 each!) as Renault are £££!. Car has been great since!. You can also try linking them out first, but i'd be confident that it's that! - CLEAN THE RELAY'S SOCKETS TOO!!
Tim, April 2009