Hi, I have a C5 2L HDI (2006) engine number BW10TED4. The car ran well when I bought it but never reached normal engine temperature. As winter was approaching I decided it was time for a new thermostat. That's when the problem started. Car ran fine for around 7 miles (until the temp gauge got up to around normal) then setting of from the lights the car would start to pick up and then hesitate for a second, then pick up as normal, if you accelerate slowly its ok but normal acceleration would cause the same dip in power. If traveling at a constant speed and it starts to loose power ( only for a split second or so) either easing off slightly or increasing power slightly sorts the problem for a short while. If you put your foot down hard it would fly but left a dense cloud of black smoke behind. I tried changing all the filters (Citroen filters used). But did find small shreds of metal in the fuel filter. So a new HP pump was fitted (no lift pump in the tank). Citroen diagnostics said it was the EGR control valve and the supplied the unit that sits on the rear left of the engine, it supplies a vacuum to the turbo. The EGR valve on my car is at the rear right of the engine and is electronic. I removed the EGR valve which looked newish, smooth in operation, and a good valve seal. No vacuum pipe on mine its electronic. Checked round all the vacuum pipes etc and could not find anything amiss. Took it for a run and I had lost turbo. Checked over all the connectors and found one that looked connected but had not clicked in. Took it for a run, turbo is back, no black smoke, but lacks a bit punch. It has run fine all summer, just a bit short on kick when you want to overtake but turbo is working.. The first frosty morning and we are back to the original problem OK when cold, when engine at operating power - momentary loss of power when setting off, accelerating, and cruising at around 65mph.But no black smoke. It feels like the fuel supply is turned of for a second and then back on. It seems to be temperature related. The EGR valve I am told only operates when the engine is at operating temp. Also I have two pipes from the turbo to the inlet manifold. One direct from turbo to manifold ( when engine cold ) The other pipe turbo - cooler- manifold (engine hot). I am using diesel from a BP garage. Anyone any suggestions as to what is causing the hesitation. Thank you for your time. John
