Hi Nick I don't have an answer, but I have forwarded it on to Darren who's hopefully bored and can help you out! However, I have some comments: >> Checked Frequency valve `buzzez' The Frequency valve's duty cycle will not change when te engine is cold, but should still buzz. >> Checked Supply voltage and earth return at Fuel Control Pressure Regulator. I think I'm right in saying that the electrical supply to the CPR is merely for the internal heating element, with it ot working, the fuelling will be a bit rich for a short while during warm-up. >> Adjusted Fuel Distributor flap so frequency valve duty cycle oscillates between 32 and 45 on a dwell meter. (Note I have re- plugged the adjustment hole when taken a reading). This is something you must've done when it was/is warm. >> When the engine is warm the engine idles pretty smooth, varies +/- 50 RPM at approx.780 RPM. As we have recently established, the engine should not hunt at all, even when cold. The reason for it is most likely tired intake manifold seals creating vacuum leaks. >> The engine speed does drop when the air conditioning/ heated rear window and lights are put on. This could be caused by the idlespeed valve being "maxed out" due to vacuum leaks elsewhere in the system. Is this true for when it's hot? >> Can anyone advice anything else I can try before I buy a replacement idle speed ecu? Borrow someone else's for 5 minutes and see if your car acts any differently. Warm up problems are very often caused by the control pressure regulator - Claire and Dave have similar troubles with DGS. Sorry I can't be of more specific help, but I should be getting a copy of the Swiss Renault manual soon (the PRV with k-jet, idlespeed system and cat in europe) >>Apparrently the same ECU could come from a Volvo 200 and 700 series with the PRV engine. Correct. My donor engine is from a 760 Martin -------------------------------------------------------------------- mail2web - Check your email from the web at http://mail2web.com/ .