Code P0172 & P0175 on Mercedes W212 E-Class - MAF Sensor & Throttle cleaning

I got a check engine light with some rough engine idle on my Mercedes W212 (E300 2011) a few days after replacing an ignition coil: Checking with an OBDII scanner it shows codes P0172 & P0175 for engine rich condition on bank 1 & 2. Fuel trims on both banks showed below -20% (long term + short term). O2 sensor readings for both banks were similar to each other. Fuel pressure was stable with the ignition on and engine off. I decided to first clean the mass air flow sensor (MAF) and the throttle and see what happens (both were very dirty). Cleaned the MAF and throttle with electronics spray cleaner since I couldn&find MAF and throttle spray cleaner until a week later. After cleaning, the Fuel trims on both banks went down to -15% but the check engine was still on. After driving the car for a few days (engine was a lot smoother) the check engine light turned off on day 3. **Update: The check engine light came back on 2 weeks after it was gone with the same codes. At this point I suspected the intake manifold or the MAF sensor. Since I didn&want to just throw expensive parts to fix the issue and couldn&check if any were the problem I decided to go to a Mercedes shop for diagnosis. Initially, they told me I had a bad intake manifold and wanted to also change the spark plugs and 2 coils. Since they seemed to know what they are doing I gave them the green light to fix it plus the labor was reasonable at the time. When I came to pick up the car it turned out that they also decided...