Slight misfire, any ideas

[AirconAde]

Ok Chaps,
I have a slight misfire on my 4.0 it's a very very slight mis but it is enough to make the gear stick shake at idle.

I can't pin point one cylinder that's at fault, if you pull plug leads one at a time the engine misfire gets worse.

So far I've changed the dizzy cap(lucas),rotor arm(lucas),plug leads(bosch),plug extenders(clevor trevor non restive one's as beru one's no longer made?) plugs, 7ecs gapped to .9.

The timing is set a 8 deg with a strobe.

I did notice that the nearside spark plugs were more sooty than the off side.

I've checked both lambda probes and they are switching although I've only checked them with a DVM not a scope.

It is running a tornado chip but was the same on the standard chip. I have also tried it on the non cat map and the misfire was still there.

fuel pressure is at 35 psi at idle.

I've set the base idle and the stepper motor is working fine.

I have noticed that the rev counter is a bit jumpy but is that a trait of early chim's?

What do you chaps think?

Cheers Ade