Alright, since I'm the only one who talks here, I'll go on
Booked her with a "doctor" on Monday but:
I've disconnected MAF with no better results, when engine is warm and idle is erratic, with the maf disconnected it dies, so MAF it's ok (it's a Bosch, not a cheap ebay thing).
I've also notice that the erratic idle is ONLY and I repeat, ONLY when the engine is warm/hot (around 90). Also today before taking her for a nice bath I've noticed that the rear bumper, near the exhaust (just above it) was a little black, so that means it smoked too much.
Beeing the fact that it only does this when the engine is warm/hot and that I had the smoke mark on the back of the car, I'm thinking lambda sensor is dead? I know the sensor starts working when the engine is hot (the sensor is working at 600-700 degrees as far as I know) so all this makes me thing it's faulty.
A dead lambda can affect performance as well isn't it? It does not feel like a 155bhp engine but I'm not sure about that, maybe it's just me... never driven other 156s to see the difference.
Edited: when engine is cold, starts well, goes around 1100rpm and then gently goes down around 800 where its rock solid.