Pop out the bank1, drivers side coilpack
You're looking for
any of the following:
1. Evidence of water or oil in the plug wells, especially the middle one, plug 3.
2. Cracking or corrosion on the visible surfaces of the coil pack.
3. Loose plugs, again plug 3 in particular.
4. Any sign that the wiring to the coil pack plug is breaking down, either brittle or corroded.
Solutions, see maintainance guides for how tos:
1. If water, dry out and also re seal the scuttle.
If oil then the cam cover gaskets need doing along with the breathers.
2. Replace the coilpack, they can look pretty shabby and be fine, but if alot of rust
and cracking replace it.
3. Tighten the plugs.
4. Last resort this one, and for now unlikely, new loom.
For peace of mind if you find 1,2 or 3, check the other side