Engine hesitant at about 4500 revs

[David Boyd <john@dboyd.demon.co.uk>]

My '89 Audi 100 2.0 runs fine except that the engine starts to hesitate
and surge badly at around 4500 rpm. Lower or higher than this band, it
is OK.

Can't see anything obvious, but if anyone has any advice before take it
to the dealer, would much appreciate it.
-- 
David Boyd
mailto:david@dboyd.demon.co.uk
Cumbria, UK