Casey Imports CASEY Auto Group Costly repair bill, but problem remained. Newport News, Virginia

I was visiting Virgina from Minnesota when my Audi A8 started missfiring.  I took it to Casey Imports on 1/3/2012.  The following is copied from the invoice:

OWNER STATES THAT CHECK ENGINE LIGHT IS FLASHING AND STAYING ON FAULTY IGNITION CONTRO MODULE. PART NUMBER IS 4D0905351 FOUND DTC'S FOR MISFIRES ON ALL CYLINDERS, VEHICLE WAS NOT MISFIRING AT TIME OF DIAGNOSIS, HOWEVER THE TECHNICIAN FOUND THAT THE IGNITION CONTROL MODULE WAS FAULTY, INTERRUPTING THE SIGNAL TO THE IGNITION COILS.  REPLACED CONTROL MODULE, CLEARED DTC'S, TEST DROVE VEHICLE.  SYSTEM CURRENTLY OPERATES WITHIN SPEC.  ADVISE CUSTOMER THAT IF INDIVIUAL MISFIRES OCCUR IN THE FUTURE, REPLACEMENT OF IGNITION COILS MAY BE NECESSARY. ALSO RECOMMENDED SPARK PLUGS. CUSTOMER DECLINED.

The total bill was $614.79

I didn't have the plugs replaced because they were replaced the week before my trip to Virgina.

The next day I started my trip home.  After about 3 hours while in the mountains, the misfiring returned.  I limped along for 30 miles to the first available exit and filled with gas.  The engine then ran better with only an occasional misfire indicated by the blinking engine light.  I managed to make it home but my gas milage was only 24 mpg which is down from the normal highway 29 mpg that I usually get.

After home, I had my normal mechanic at Tommy's Garage (in Hopkins, MN) look at my car.   In less than 15 minutes he found a vacuum leak that he fixed by just shortening a rubber hose and reattaching it. I am now getting over 24 mpg in my normal city driving and the engine light has stayed off.