My car keeps loosing power when driving. l have changed the fuel filter as recommended but the fault still persists. Any ideas what this could be? When the car looses power it feels likeit dips and l have to push the throttle right down to get the car going again, it does not stall at anytime and idles perfect.

cat may need regenerating, if you are in a breakdown service give them a call for advise.

sounds like air flow meter try disconnect the plug on the side and it should default the unit to the e c u try test run

did it have any power to begin with?

Could be ECU issues we had a Vauxhall Zafira that did the same thing, took it to vauxhall and they plugged it in and sorted it! worth a try if its not ECU they will be able to tell you what it is.

If u disconnect the air flow meter it will cause the car to run worse.

This sounds very much like a vacuum problem. It is not uncommon for vacuum pumps to start sticking on the Xsara HDi. This will cause a lack of vacuum, which in turn causes the turbo to operate incorrectly causing a loss of power. The wastegate of these turbos is normally open, which means it requires vacuum at idle to close the wastegate, & it kills the vacuum supply at high revs to open the wastegate. This also means in the event of a problem the turbo does not overboost thereby protecting the engine.

So if ur vacuum pump is producing a poor vacuum ur engine ecu cannot control the turbo, which produces ur symptoms. Usually giving the engine full throttle will cause the vacuum pump to start working properly (as it is driven directly of the end of the camshaft) & so u get ur vacuum & therefore ur boost back.

You can verify if this theory is correct by putting an abnormally high demand for vacuum on the engine & see if the vacuum pump can cope.

Whilst stationary have the engine running & pump the brake pedal until it goes hard, then keep as much pressure on the pedal as u can. The pedal should start to creep away from u as the vacuum pump builds up the vacuum pressure to the brake servo.
If the pedal does not creep then u have a vacuum problem.

Whilst driving try accelerating without full throttle & then braking hard. Do this a few times & see if the brake pedal gets hard or the acceleration gets sluggish. Both would be signs of loss of vacuum.

If these tests indicate a vacuum problem (do them a few times to be sure) then u can be sure that the pump is getting sticky. A new pump is easy enough to fit & will probably cost around £100 from Citroen. Alternatively try lubricating the pump by disconnecting the vacuum pipe outlet & spraying some WD40 in the outlet whilst the engine is running. This may help temporarily.