This has probably been discussed before,but as there are so many poor idling issues around,it is hard to get the same situation.
My 2003 GTV last week out of the blue started smelling rich,then I could virtually watch the fuel gauge go down.Now it intermediatly idles rough and misses big time on acceleration.So over the weekend,I changed the front and back bank plugs(its done 208k-so it was needed anyway)and the fuel filter,and tried some 100 octane fuel to clean things up.I have just driven 40ks to work.90% of that was freeway driving and still the same.Started off great.Had a bit of a shake and miss at a set of lights(had to put in nuetral to avoid stalling),then was fine again.Maybe Im on the wrong track,but I did notice when changing the plugs that the spark plug tube boots on some cylinders where dripping with oil.Could this be shorting the spark intermitently as a spark follows the shortest route.Also is there a seal between the rocker cover and the tube that the lead boot goes into or does the boot itself seal between the cover and tube,hence a new set of leads may help.I have also notice recently a bit if very slight resistance for the 1st cm or so on the accelerator pedal,with "step" when pushed a bit harder.The oxygen sensor ,throtle sensor visually look clean and ok?The car idles at the correct speed.

usually if you have had a lot of oil in your tube seals its probably a good idea to replace the leads as well, could try cleaning up the tip of the leads, but usually you will find the oil soaks in to the leads a little

I would hedge my bets on a dirty or faulty injector not closing correctly, I have seen these come in where you could barely see the spark plug for oil and the car still ran ok.

When replacing leads we recommend genuine ones only, have had way too many issues with aftermarket ones.