Misfire is most likely MAF and/or throttle body sticky especially at that sort of milage. Give both a clean, before you fork out £200 on new MAF Good articles out on net.
Essentially for 166 V6, (assume similar for 156 V6?), take the air box (plenum chamber or some sort of reverb tuner?)off the top of the venturi tube (black plastic bit of drainpipe 6" long that sticks vertically out of air filter box) by unclipping the fancy jubilee type clips and unscrew 2 torx screws that hold sensor in middle of tube. These screws have a security "nipple" on them so you can use a pair of pliers or small plumbing type wrench deftly on the edge of screw head. The tamper proof screw bits are obtainable from Machine Mart shops for about £10. http://www.machinemart.co.uk/search.asp?q=tamper
Clean the little passage way which disappears into the sensor tip. I used a combination of electrical contact solvent cleaner and a video head cleaner, both from Maplin
about £2.50 eash. Flood the chamber several times and if need be VERY careful use of a fine very soft small artists painting brush. Don't expect it to clean in one go. Remember this dirt has been cooked on at 300deg C!
The solvent needs to be high alcohol (isopropyl) so it doesn't melt plastic and leaves no contaminants itself.
Link to article and others: http://www.alfa156.net/fr_index.html?/info.html
Also good link:
Interestingly I was talking to a Bosch dealer when I was trying to source a new one in case the clean didn't work - the Alfa part number on the device does not show up on any data base. The Bosch dealer quoted me £280 + vat, more than the Alfa dealer. He said that this was a new original Bosch item and that a huge number of units on the market, even those fitted by official Alfa dealers are reconditioned units.(hence the part in my car with no Bosch part number) Eurocarparts do a surcharge on their "new" units for VWs etc so they must recycle them.
How long does a MAF last? Nobody really knows from what I can tell.
An oiled type "free flow" filter such as K & N will probably contaminate it far quicker.
Bosch part number is 0 280 217 531