Hi Craig we had a Laguna with similar symptoms which i chased for ages. I eventually located the fault to the pin connectors in the ecu multi plugs,ever time I back probed the throttle body connector at the ecu it would work and give me correct values! So I stripped the (with much difficulty)the wires out of the plugs and what appears to happen is the pin connectors lose their tension, I tried to tighten them up but as I pushed a dummy pin in it just opened up.Piss poor design and materials! Hang on it's a Renault! Good luck Craig,regards Nigel.