Do you know which cylinder is misfiring, or is it random? It sounds to me as though there isn't enough fuel, either because theres a problem with the fuel delivery, or because theres too much air getting in.

What happens when you increase the idle speed slightly?

I still think you should check the EGR valve, it is held by a spring which gets weak over time and the valve can sometimes not close properly. Carbon deposits also make this more likely. Intake manifold has to come off to gain access.

I'd also check around the EGR valve for any air leaks - mine has one at the base of the valve caused by an old o-ring I haven't gotten round to changing yet.