jumping

Hi after a lot of work I'm on my last job, poor running, the discovery is a rd5 auto 1999, it's jumping when driving, at low speeds about 20 mph and at cruising speed 55/60, there are no fault codes, it's like it drops a cylinder for a split second, it drops about 300 400 rpm then comes back, am I right in thinking the fuel system because that's not covered by diagnostics, I did the injector seals about 6 months ago(genuine) thanks Phil

Had problems with mine for months. Random "missing" and poor running around 70mph replaced injector loom twice, even replaced fuel pump. Problem FINALLY identified as the throttle pedal. It has a tiny potentiometer stuck on. This was the cause. £500 it took to find that. No fault codes, nothing. Pedal cost nearly £100 to replace.

Throttle pedal assy - £295 from main dealers as of a couple of days ago!