Ok, well you have done the usual culprits and if it is still doing the same.... Next things to try:
I'll try and keep this as cheap as possible m8.
1.Remove,check/clean coil packs & connections (remove one at a time to save mixing them up). look down the spark plug wells for any fluid/debris/oil, they should be clean as a whistle.
2. Do you know when the spark plugs were changed? They last a hell of a long time but not forever!
If in doubt, remove them one at a time and check them accordingly for carbon/soot/oil.wetness etc. Are the gaps precise?
3. Moving back to the air intake system.... What are the spring clips like? i.e. can you move the MAF body by hand with the clips tight? If you can then they are too loose (dirty, un-metered air under light throttle) and may I suggest removing them all and replacing with jubilee clips that are much more secure.
If that doesn't resolve it, then I hate to say it but it is maybe down to the lambda (O2) sensor giving a false reading to the ECU.
It is possibly but unlikely, the throttle body itself ! Remember what I said about what goes in must calculate with what goes out.
Get it on an Alfa diagnostic to make sure though.
Before you go ahead and buy an 02 sensor, it may be worth your while actually taking the old one out and giving it a good clean with carb cleaner, the same with it's connector plug further up the wire (electrical contact cleaner).
That way, you are eliminating two more possibilities... electrical contact fault and faulty O2 sensor. A clean often works but unfortunately it is mostly a temporary solution to replacement. But it will let you know for sure.
Now the bad news.... O2 sensors can be a pig to remove, the sheer heat that they go through can virtually weld them in so heating them up can often be the only way to remove them. Local tyre & exhaust centres are very adept at getting them off.
Throttle bodies can be a pain, not to remove but getting the seal right and ancillery parts back on in perfect position.
Again.... If you are going to remove to replace, try a second hand throttle body on to keep the cost down or at the very least clean your original thoroughly once off.... I don't honestly like making suggestions that cost another owner money....
After that m8, then I can only suggest a full diagnostic and possibly a timing check (it may be out ever so slightly) PM Smaky if that's the case, he can help you get it spot on
Good luck m8 and I really do hope you get this sorted soon