Engine - slight misfire

[MML]

I'm having a bit of trouble with a misfire on my car.
A bit of background - a few months ago, the distributor cap, plug leads, plugs, and rotor were all replaced - the problem was the cap was knackered (spark jumped across contacts) manifesting itself as a rough shudder when I drove.

It started misfiring again a couple of days ago. It's a subtle misfire this time, it's idling good but sounds lumpy when when you rev the engine.

I had someone take a look at it and it was found that one of the plug leads wasn't seated correctly. The small screw-on tip on the spark plug had loosened itself and almost come off, pushing it back in sorted the problem. I thought that was the end of it, but driving back home from a show yesterday, it started again; same as before, subtle but definitely there.
One thing that was found - the ignition coil was quite hot (too hot to the touch) and was replaced. This didn't fix the problem though.

There don't seem to be any vacuum leaks. The spark is good on all cylinders. I noticed the ballast resistor is hot - is this normal?

Anyone got any thoughts?

Here's a video from before the plug lead was reseated. It's not just quite this bad now.

https://youtu.be/KNH3EKB3TbE

[MML]

Forgot to mention, I'm going to get some injector cleaner and put it through the tank. If that doesn't help I'll get the injectors tested as well.

[David T]

The coil should get hot and so should the ballast resistor. Pull the plugs and check them. Make sure they are all gapped properly, they are all the correct type, and they are all the same color. Look for any signs of leakage. We have seen the platinum ones leak so don't use them.

[Bitsyncmaster]

Hard to tell what may cause that problem. Misfire is mostly an ignition problem. Verify none of the plug wells have water in them. If you know another owner, maybe borrow his ignition ECU to verify that is not the cause.

Of course all the basic fuel checks, pressures and spray pattern of injectors should be checked.

[MML]

Dave and David - thanks for the reply guys. Will get my mechanics to investigate. Plugs are a few months old but will check them regardless.

Was recently advised to replace the fuel filter, as to the best of my knowledge mine's still original - could dirty/contaminated fuel cause this problem? It only appeared after refueling a few days ago. Or maybe it's just coincidence?

I actually have a new filter here in the garage.