07 traffic misses intermittently?

My 2.0dci115 trafic (2007) with approx 72000 has been great up until it came back from my local garage after PSV test. had lend of my dads van for a few days until i got road tax sorted on my Trafic. basically it sat at his house for 5/6 days. I put some diesel in it (all through a proper filtered funnel) and decided to drive it the 4Mile journey home.3 miles later i felt what was like a flat spot under acceleration) so i kept a watch for it but it is happenening regularly whether you`re cruising alongt at 50/60mph or 30 or 40mph. It has got more regular and STOP light has come on but that is normally when i try to force accceleration. ease off or drive very carefully and it just misses. Engine management light on & the heater /water in filter light on. Van had new filters all fitted whilst in for PSV test. Sealey Diagnostic machin giving me Df050 and DF 056. DF056 is an air flow problem apparently. Air flow meter taken out and cleaned but no difference.how would i know if it`s goosed without exchanging it? Any ideas on my dillema folks?