I replaced the air-filter and cleaned the MAF with the recommended CC cleaner. I checked for vacuum leaks, but do not know how or where to check so I only looked at tubing I could see without removing any parts or covers. I looked at the fuel pressure regulator - took the vacuum hose off and noticed the smell of gas in the tube, but was not able to blow air into the valve.

I found the following in the service CD (Copyright Daimler AG 11/4/08), "Note regarding mixture preparation self-adaptation: ....Should malfunctions occur in the form of:
-Intake air leaks.
-Injector wear or carbon build-up.
-Engine wear.
-Contact resistance in MAF sensor.
-Defective diaphragm pressure regulator.
-Defective purge control valve."

Do I need to check every vacuum hose for a leak or are there specific "intake air" connections I need to focus on?