TD5 runs light

In the process of buying a 99 TD5 discovery. In March the fella put it off the road to do the head gasket and the power steering pipe burst on the way home scunnered with it he parked it. i am in the process of buying it (worth the money) have it up and running ready for the test but the engine is running light as if it is getting to much air. It does not smoke and starts very easily. its just fluffing on tickover and is down on power when driving you sort of have to rev the guts out of it to get it to pull .... any ideas please

Sensor unplugged somewhere or possibly air flow meter faulty? If the head has been off was the timing set properly after?

she can pull 60 mph not to badly and starts perfectly so thought it couldnt be the timing will check sensors in morning ..... how do you check the flow meter sorry a bit thick on these engines more used to 300

Turbo not boosting?

Maybe a bit of fuel starvation? Is the pump healthy with no blockages? Is the filter reasonably new? And not coming loose? I've had symptoms like this when I was about to run out of diesel. Is there much fuel in the tank? Some of them have tiny strainers where the pipes screw into the filter bracket which can clog up over time.