The plugs don't look old enough to replace - check the gap.
Check your plug wires - When it is dark, mist(spray bottle/plant mister) the wires, and look for arcs.
If your oil isn't coffee colored, and your coolant doesn't have black spot floating in it, I would lean towards needing new valve seals.

BTW...are those non-resistor plugs? Who made the wires? (see sticky about non-resistor plugs)

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D