If the Idle is surges when it's cold out it's likely that the Idle Control Valve is dirty. I replaced mine ($140 part) and it's much smoother now. I overhauled my Vanos seals thinking that they were causing the problem and although it helped performance, the problem continued until I swapped for a new ICV. Very common problem with the M52.
Last edited by DPP528; 10-11-2012 at 08:32 PM.