revs not dropping. HELP!!! please

hi,
ive got a mk1 with a mk2 16v lump.
my car idles fine and runs smooth. untill you change gear when the revs pick up as soon as you dip the clutch in, it picks up about 2-400 rpm and then takes a while to die. i thought it could be a sticky throttle cable but cable runs smooth,
any ideas tips or solutions would greatly help

not so much the cable as the throttle itself. take the boot off and see if the throttle opens and closes nice and freely.

yer it all runs smooth. cleaned it out a bit and still the same problem . could anyone help as this is really annoying me now
lol