My '82 BMW has K-Jetronic. I cleaned the airflap and "throat" in the airbox with carb cleaner. I was replacing the rubber bellows between the airbox and intake manifold and noticed the aforementioned internals appeared to have a maple syrup-colored coating around and on it.
K-Jetronic systems are VERY sensitive to vacuum leaks. Any "false air" that bypasses the airflap will lean the mixture going to the cylinders. Mine is tuned perfectly (and all hoses replaced) and I will stall the idling motor if I unscrew the oil filler cap. I've heard the same is true if I would pull the dipstick but I haven't tried that yet.
If the rubber boot going to your airbox is not soft and supple, replace it. You'll have to remove it to check the cleanliness of the airflap anyway so you'll have a good look at it.
Here's a good site on the theory:
http://www.auto-solve.com/mech_inj.htm#MFI08