Just installed the X51 airbox, RSS Plenum, Suncoast headers and FVD mufflers to my car. After driving a distance of 50 km I got a CEL message. I stopped the car called the workshop and they said that if the engine on idle went smooth there should be no problem. The idle revs moves between 900 and 1300 revs. When driving in high gear with low revs (below 2700) the car was lugging a bit. Smooth and responsive at high revs. Water and engine temperature as normal, so I drove 450 km back home.

Since there is no Porsche workshop in my town, I need to find what this could be.
Could this be mass air sensor problem? What do you guys think??

 

Sounds like you have vacuum leak or unmetered air into the intake. A erratic idle is almost always a vacuum leak or unmetered air after the mass air sensor. Recheck you connections and make sure they aren't loose and leaking.

Dave