Could be the seal between the DISA valve and intake manifold. Cold weather could cause the seal to shrink enough that now you have a vacuum leak. Just fixed my P0171 and P0174 error codes (lean bank 1 and 2). Originally I took the DISA valve off the intake manifold but the valve wasn't rattling and the test for vacuum for the flap WAS O.K. SO I put it back on, but I was still getting the Service Engine Soon (SES) light. One cause for cause for the SES is a vacuum leak and since I didn't have a smoke machine I decided to use what I did when I use to race Triumph and Lotus in the 70's and 80's. I made a tool to listen for vacuum leak. The tool consisted of a funnel and a length of hose. I connected one end of the hose to the funnel and use the other end of the hose I use to probe around the engine compartment. I held the funnel to my ear and listen for vacuum leaks at all the known places. When I placed the hose by the intake manifold and disa valve I heard the vacuum leak.

Removed the DISA valve and noted that it came off fairly easily (another sign of a flattened seal). I removed the old seal (why BMW engineers didn't use a standard O-ring for this application I would never know) with a pick, jeweler screw drivers and a brass brush (don't use a steel brush), if you don't have a brass brush, use an old tooth brush.

Fitted an O-ring (62mm x 55 mm x 3.5mm) to the DISA valve and when I went to install the DISA valve it took a little more force to to push it into the intake manifold. Started the engine and clear the previous SES. Went for a drive and a fill up and check for fault codes on my son's tablet with the Torque App. NO fault code found. Look at the Long Term Fuel trim and it was within the guideline. The idle was rock steady at 700 rpm.

Hope this help you.