Intermitten misfire 16v '89

[Diluxe]

right, have a misfire on my golf that intermittent, some days its really bad other days it will misfire on the odd occasion. What i've noticed is that the Revs bounce up/down 500 rpm on there own when it happens. seems to happen more in the low half of the revs and is more evident under a load but i guess that becuase there drive going to the wheels

to try and get to the bottom of the problem, i've tried/replaced ;

1)2 different ecu's from working cars
2)metering head
3)igntion coil under a year old
4)dizzy again under a year old
5) sparks plugs ,rotor arm, rotor cap less than 3K miles
6) checked vacuum hoses all seem fine
7)disconnected the throttle switch to make sure it wasnt that misbehaving
pulled the ignition cables out one by one all had an effect on the idle, so i guess they are ok

when its not misfiring the car goes like a rocket

any help would be greatly appreciated 

cheers

[Ryan]

i had exactly the same problem in mine but mine was cutting out but i have changed the dizzy for a spanker new one from gsf and replaced all the vacuum hoses and metering head and it seems to work fine the now.

[Diluxe]

i've tried another dizzy and same result,

with the Vac hoses, i have 2 that go off into the bulk head somewhere & 1 thick black one that goes to the brake servo, all seem fine , from what i can see, but i cant see the one terminating at the brake servo , am i looking correctly at it or do i need to get under the car, where do the two that go into the bulkhead go off too?

[GT3 Turbo]

check to hall sensor loom terminal for corrosion.

[Gambit]

yeah bouncing rev counter and misfiring points to the hall sender!! the wiring for it can become very brittle over time.

[Diluxe]

tried again another dizzy today, but no change on the misfire, did the timing again & noticed that when you put the conductive coil thing on the ht leads, i get the timing light flashing correctly on leads 1 & 2, but out of time completely on 2 & 3, should i be able to do timing  off any of the HT leads?

cheers