MAFs ECUs and problems

[Mja]

Well, where should I start! The car is a '01 Polo Estate 1.9 S TDI. Ever since I've had the car the performance has not been up to TDI spec. The acceleration is lacklustre, the car has been checked with VAG-COM and the opinion was that the turbo was doing as requested, but the Maf was probably not.
So I eventually got round to getting a new Maf, fitted it and disconnected the battery for 4 hours to reset the Ecu, and the first thing that I noticed when cold was that the idle dipped every 5 secs or so. The engine under normal driving/gentle acceleration was lumpy/jerking etc. But under hard acceleration, bloody hell I'd got a TDI at last, way quicker than before fitting the Maf. But this was accompanied by lots of smoke.
Having heard that the Ecu checks everything every 200 miles, I thought I'd give it that long to maybe sort all this out. But 250 miles later, nothing had changed except that the fuel gauge was way lower than normal.
I then disconnected the Maf, and my car was back to how it was before fitting the new Maf, proving that the old Maf was doing nowt.

My questions are:
1 How come the Ecu didnt do the biz and sort out the performance problems
2 Is my Ecu stupid and wont learn
3 Will disconnecting the battery overnight do any good

Any help would be appreciated as I've now seen the difference in performance that a "working" Maf can make.

TIA