My e46 didnt have power when it was cold after the start, was having" hiccups" as you mentioned. The reason being was a lambda probe/ oxygen sensor. After putting in a new one i had no trouble what so ever.

hope it helps!

http://www.obd-codes.com/p0171

A code P0171 may mean that one or more of the following has happened:
The MAF (Mass Air Flow) Sensor is dirty or faulty Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
There could be a vacuum leak downstream of the MAF sensor
Possible cracked vacuum or PCV line/connection
Faulty or stuck open PCV valve
Failed or faulty oxygen sensor (bank 1, sensor 1)
Sticking/plugged or failed fuel injector
Low fuel pressure (possible plugged/dirty fuel filter!)
Exhaust leak between engine and first oxygen sensor

not really sure if any of this relates to your problem though.

listen man the best place to go is forums for your car just google it and read around or even post and ask the bmw car fanatics there. they would be able to diagnose much better then most of these people including me. and this is solely because we dont own one just sayin and
forums is where the knowledge is at.

Sorry it took me a while to get back.

But I am also thinking this.

Do the carb cleaner, or ether trick. Spray little puffs around the engin3 bay and see if it influences revs at all.

This post was edited by OldAndyAndTheSea on Feb 26 2013 05:37pm

and keep your arms, legs, and body away from the mist of the ether while you do this lol.