P0172 rich mixture 2005 Polo

[shuish]

My son has a 2005 VW Polo 1.2 engine code BMD.
It brings up P0172 rich mixture fault code after a few days and puts the engine light on.
It still runs lovely with no misfire or loss of power.
I have fitted another cylinder head with new ex valves and guides as no3 cylinder valve guide was worn badly.
I have also fitted a new cam chain and tensioner.
I have Vag-com diagnostics and can see the fuel trim and block 32 always shows a negative figure (-15% approx)
I have replaced coolant sensor , Map sensor and 02 sensors.
I have also checked inlet manifold vacuum and it reads 17in/hg at idle.
It now starting to do my head in.
Any ideas would be appreciated.

[alexperkins]

Are the lambda sensors measuring properly?

[shuish]

Yes they are , they have both been replaced and made no difference.

The long term fuel trim is always a negative figure , like -15%.
The short term fuel trim seems ok alternating between positive and negative.

[shuish]

I have fitted a new VW fuel filter assembly that is rated at 3bar and it has made a big improvement on my LTFT figures so i may of finally fixed it.......


Someone had helpfully fitted the incorrect fuel filter .....

[alexperkins]

Excellent. Glad it's sorted