Always a good idea to disconnect the battery when installing anything electrical. One, reduces risk, two, resets DME. It's very easy...10mm socket and disconnect negative terminal in the trunk.
First...take logs and see what your trims, AFR, and fuel pressures look like.
Second, swap coil packs and see if the problem follows. If it does, change coil packs, if it doesn't...
Third, swap plugs and see if the problem follows. If it does, new plugs, if it doesn't...
Forth, swap injectors.....
2008 AW E88--2 years on 100% E85. Too much to list..
2011 AW E90--Tune--Stage 1 Turbo--FMIC--DP
2013 Mini JCW--Tune