When I started my '08 Vanden Plas this morning the engine revved up to over 3500 RPM, didn't respond to the gas peddle and then dropped until the car sputtered and died. It did this three or four times in a row. My code reader simply said "misfire on all eight cylinders". To me it seemed like a throttle issue, and then I remembered that what I thought to be a sticking throttle on my last XJ8 turned out to be a dirty Mass Air Flow sensor, so I cleaned the air filter, removed the Mass Air Flow sensor and brought it into the house to spray it with Mass Air Flow sensor cleaner and upon inspection I discovered that a spider had spun a very sticky and voluminous cocoon inside the Mass Air Flow sensor. It took a bit of work with the vacuum, a cue tip, and lots of solvent to get it clean, but when I reinstalled it - voila - my Vanden Plas runs like a charm again. How a spider got past my air filter and into the Mass Air Flow sensor is beyond me, but the moral to the story is to inspect/clean the Mass Air Flow sensor when you have the symptoms my car experienced on cold start.

 

Sorry for my terminology - "Mass Air Flow sensor" is technically a MAP (Manifold Air Pressure) sensor.