Throttle positioning sensor.
It is the red thing on the side of the throttle body.
I made scorings around the position of the 2 bolts that hold it in place, as it is factory set and needs to go back in the same place, otherwise it will totally screw things up.
When I took mine off, there was only a small patch of clean metal that was making the contact on the throttle body. Dont know the name of the thing it makes contact with. Cleaned it off with a wire brush and put it back on.
It made an immediate difference.
Also check that youre not getting oil in plug wells. If you are the rocker cover gasket has gone and the oil will be fouling the plugs. Easy job to do, makes a difference on the running of the car. Well it did in my case, cos it had gone round 3 of the plugs. Dont use patent gaskets!