I personally don't think you need an air flow sensor. You mentioned that you have about 100k on the car. I would like to know how your sensor look like. Is it the one with the plate on top. Let me know and I will explain things better on how to check it. Also, I don't understand how a fuel injection system is cleaned. I am a test enginner in fuel systems working for a major German company. and anyone tells you that it can be cleaned, he is FULL OF CRAP. The best thing you could do to the injector to clean is remove the carbon from around the needle (for digital injectors). I run fuel delivery maps on injectors out of engines every day. Anyway, give more details to better understand your problem.
1993 190E 2.6
Advanced Diesel Systems Test and Research Engineer