i warned you about fitting that lawnmower engine well in advance to the conversion!
mines doing the same thing mate, i changed the speedo cable, road speed sensor, cleaned the TB, and iscv, changed fuel filter, cleaned injectors, reset ecu.
still does it. think i need a new iscv...! if u take it to renault they will tell u, i just dont fancy paying £35 just to connect it to a pc...!