Gen 3 diesel misfire/rough idle

[mwh]

Hi
I am asking on behalf of my friend who has a gen3 diesel surf.He used agricultural diesel and now idling really rough and misfire.He adjusted the revs at higher position now its idling is improved but misfire still there.Any suggestions guys?

[Predictable Bob]

Fill up with proper diesel, change fuel filter and then give it an Italian tune up ...

i.e. chuck in a WHOLE bottle of redex and thrash it for 30 minutes !