I am having problems with this Skoda giving fuel trim fault p0170
I am getting 398 hpa manifold pressure on actual values - around 17 on vac guage which seems not quite enough. I have used smoke pro and no leaks evidant. It runs fine but fuel trim is at about 4.5%
ESI says the valve clearances are hydraulic but they are adjustable, and had no clearance so we removed / reseated the valves reassembled and still the same !!!

Only 45,000 miles and 1 owner.
I have also carried out engine flusch

Any Ideas would be apreciated