Hey guys, have an issue with my MX73 5M-GE which has always been there but getting worse now that it's colder.

It will start up and idle fine first thing in the mornings, and you can even blip the throttle and it seems to rev smooth enough, but once you get underway driving and apply some moderate throttle the engine will surge as if it's mis-firing but not quite as harsh as say an ignition mis-fire. Once it starts warming up the severity lessens but it is still present to a degree when it's fully warm. Sometimes the more you give it throttle the worse the missing gets and calms down a bit when you don't put it under such load. Giving it full throttle when cold/warming up (or even sometimes when warm) will make it rev and get moving a bit better (while still missing) and then it hits say 4000rpms and wont go any higher.

The plugs, leads, dizzy cap and rotor appear to be OK (with plugs being new). Have yet to check the fuel filter and pump but figured if it's fine when warm why would it be worse when cold? Could it be the ECU maybe?

Thoughts?