I recently had an experience with my Citroën C-Crosser that may be of interest to other readers. My wife noticed a nasty clattering noise from the front of the engine when it was ticking over and I had my head inside the car. After lifting the bonnet, we located that the noise was coming from a plastic housing unit near the front of the engine, but I was unable to make any further diagnosis. So we then visited our local Citroën specialist, who diagnosed a failure of what I now believe is known as the motorised throttle body. Apparently there are a couple of plastic gearwheels that operate a butterfly valve, and they had lost some teeth, or become disengaged. The awful noise was the two teethed wheels trying to move the valve, but failing to do so, although the noise stopped when you pressed fairly hard on an end cover. Anyway, it all came right in a day or two, after the part was ordered up, and fitted at a significant, but not too painful a cost (parts £216, labour £114). I can’t find any reports on the web of similar problems, and very little mention of a motorised throttle body, so maybe the item fails only rarely and my experiences were rather a one-off. For my interest though, can you throw any further light on this item Doc, and exactly what purpose it serves?
Dave Hancock

To be quite honest, David, I’m also struggling to find very much information. Such units have apparently been used on PSA Peugeot-Citroën engines for some years, in various different forms. Once they were cable operated, now they are motorised. As I understand it, the throttle body plays a vital part in the exhaust gas recirculation (EGR) process, by using a powered butterfly valve to control the intake of fresh air, according to instructions from various engine condition sensors. These days, high exhaust gas recirculation rates are required at times to minimise NOx emissions, and these high rates can only be achieved by precise control of intake air, and by reducing the ingested fresh air and at the same time increasing the volume of recycled exhaust gas. Such throttle valves are often also used at engine shut-down, to reduce engine shudder, and also, I gather, are sometimes employed during particulate filter regeneration. That’s about all I can tell you Dave, but maybe that’s quite enough.
Doc