406 Hdi erratic idle

[Frenchenstei]

Friend of mine has a 406 HDi 2.0 and it idles as if it were a petrol engine with way too much fuel so it 'hunts' dramatically and this continues up the rev range, he had it checked on a diagnostic machine and no faults were found. It was worse before the timing belt was changed, after the belt renewal it was found to be idling too high: someone had previously tensioned the throttle cable to keep it idling and with the new cam belt fitted I re-adjusted the outer cable to put some slack back in it. A garage fitted a used ECU with no change in symptom but they won't take it off for a refund (nice). Do these engines suffer from build up of carbon and stuff in the inlet manifold via the EGR valve? Fuel filter is new. Air filter is good. Revs up ok but is a pig to drive.

Any help appreciated.

Fanx - Paul

[nige65]

Water or air in the fuel system will cause erratic idle sometime filling stations with old tanks you can get water in the fuel or airgetting in somewhere.

Also check fuel pump .

Can also check fuel tank by removing filler cap as if is causing a vacuum its hard for the pump to draw with a vacuum in tank.