Hi can anyone help?

I have a 206 Y-reg Diesel. It has started 'chugging' at between
1800-2200 revs. It seems to me that it just doesn't like going slowly!
Had it serviced 2 weeks ago by a friend (reliable not like the
dealership!) and he could not explain it. I've tried injector cleaner
and it improved slightly for a day but now back to the kangarooing.

I had a similar prob many moons ago with an old metro which turned out
to be a blockage in the fuel line.

Can anyone help?