Possible Failing Injector(s)

[cawtej120]

What symptoms should I get if 1 or more injectors are failing?

the symptoms I have are :
rough idling (I have turned the idle screw up a bit)
slight missfire with some Black smoke if I open the throttle fully at a stand still
plenty of torque till about 3000 revs with a bit of a dead spot but seems to regain torque after 3100 revs (Revs are approx as I have no rev counter)
Gutless after motorway journey but after it has cooled it returns to the same as it was before with the above symptoms.

items Replaced are :
Fuel filter 1st August 2010 ( Fuel Has not run too low since, the light has come on but I only drove to the garage which was 0.5 of a mile away)
I have cleaned the torque sleeve and piston at the same time.
I did the leak off mod 30th September 2010 (got more torque now)
Fuel pump replaced 4th October 2010 (there was no change after this)

I do have a leak of exhaust Gasses from where the EGR pipe meets the Manifold as one of the bolts were snapped when I removed the pipe to replace the rocker cover gasket I shall be getting a second hand manifold from the breakers soon making sure none of the bolts are snapped this time.

the engine is still the standard 70HP non turbo DI with no other things added or removed.

[dumper]

try cleaning out the inlet ports as you plan to swop the inlet manifold and block off the egr and try some the injector cleaner it and see how it goes then

[cawtej120]

I have now noticed that I made a mistake in my original post it should read there is a leak of exhaust gasses where the EGR pipe meets the exhaust manifold. sorry for the misunderstanding.
I now have an Exhaust manifold with a small piece of EGR pipe attached which at the moment is soaking in releasing agent. so that I don't snap the bolts this time.

also today I did clean the EGR valve and throttle body as they were full of crap, this has made no difference what so ever so I may remove the inlet manifold later on and clean that.

[cawtej120]

I removed the Inlet manifold on Wednesday night and gave it a thorough clean it seems to have made some improvement but not a great deal the missfire has all but gone now but I do seem to have a dead spot every now and then still and after the manifold was removed and cleaned the van was run for 3hours yet after 12hours sat so it was definatly cold it started then stopped about twice until I sat there with my foot firmly on the accelerator but only the once as it has been fine since maybe just a bit of air in the system.

fitted the exhaust manifold this time with bolts holding the EGR pipe to the manifold which has also made a difference still need to seal the exhaust system where the mid and back box join as they are not quite overlapping enough so there is a leak there.