Welcome to the forum. I just read your post in the S-type forum under the air filter thread. I think you should consider re-posting it as a new thread under a "Check Engine Light" title or something. The "air filter" in the thread you posted in is the cabin air filter, located on the passenger side firewall and filtering air that is drawn into your HVAC system to heat/cool the cabin. Most likely, your tech was speaking of the engine air filter, located in the front corner of the underhood area. On the 2003 3.0L, left hand drive (N. America market) it is on the left or driver's side. Not sure about the 4.2L V-8.

Most likely scenario is that they started the car with the mass air flow sensor disonnected. No harm, but that will light the chk engine light. If they reconnected it before returning your car..then the light should clear after 10 starts or something like that. Not sure your location or country but in the States many auto parts stores will read the codes for you.