BMW Repair: Low Idle and missfire under acceleration, valve clearances, 3000rpm

Question
I own a 1984 323i that has a irritating problem.
The idle speed seems to me to be low and slightly fluctuating. Whilst driving at a constant speed (say at 40mph in forth)there seems to be a slight missfire although this is cured by changing into a lower gear. Under acceleration there is a definate loss of power at/or around 3000rpm. There is also a tapping noise from the top of the engine which increases with engine speed.(The valve clearances have just been adjusted).
I am thinking it is a fuel supply problem rather than electrical, do you think it could be a dirty/fouled injector or partially blocked fuel filter?
Thankyou in advance
A Coombes

Answer
you said the valves were just adjusted,was this done cold?and did the rocker pads get checked out to see if the are worn.This is a common cause of valve noise and cause lots of problems when trying to diagnose a skip.Check the cap and rotor and look for burn marks which too is common