We have a corsa that has poor performance/ running, flat spots when cold, sometimes wiil not rev up. The head has been off to put valves in it as two were burnt out but still the same. Compressions check out OK, Egr closes and opens as it should and is sealed tight when closed, valve timing has been rechecked. No fault codes logged, live data seems ok, vacuum check on inlet suggests that it is a little low at 19 inches mercury at tickover but no air leaks.
Anyone any suggestions?
Many Thanks
Jeff