My Citroen C5 is lacking power. The anti polution light comes on, engine power dies to next to nothing so I turn the engine off for a few seconds and turn on the ignition and there seems to be power again, although very lumpy. Garage thought it might be the coil and plugs. They replaced them but still the same problem. They took off the ECU and had it tested and it has come back okay, valves have been checked and okay. They are now saying they do not know what the problem is.