Have you checked the engine coolant temperature and the air intake (if you've got one) temperature sensors.

My air temp sensor was dead, cost €12 to replace and changed the duty cycle from 50% to 90+%. Re-adjusted and everything was great aside from minor hesitate immediately after hot start. New Beru plugs (€20) solved that.

And all this is on the original, 19 year old distributor cap - that's the next purchase.

Good luck.

RayH