Bad mas air flow sensors can absolutely cause misfires by causing the system
to run too lean. It is also likely to cause misfires on all 4 cylinders as
it affects all of them. MAF sensors are pretty common but not for this
issue. I have also seen faulty Coolant Temp sensors cause this issue.
Especially on cold startup first thing in the morning. What color is the
coolant temp sensor in her car??? If its the black sensor I would recommend
replacing it as they are well known to cause many problems & have been
changed to a newer green sensor.

I would also recommend checking all the vacuum/PCV hoses under the front of
the intake manifold as they are prone to oil contamination which causes them
to go soft & split. These cause air leaks which also can cause misfires on
all cylinders until they get bad enough to cause an adaptation code.

Considering you had misfire codes for all 4 cylinders you need to look at
something that affects all the cylinders rather than things like coils that
usually affect on single cylinders.

Hope this helps.

Craig

You are correct.  However, even the improved coils seem to be
troublesome.  For example, our 2002 Passat had all four coils replaced
back in 2002 or 2003 when the big coil disaster occurred.  However, it
later developed (around 55K miles) subtle misfire problems which
Woodchuck correctly diagnosed as two bad coils and which took four trips
to the dealer before they figured it out.

If I remember correctly that software flash was a TSB & not a recall so if
the car is out of warranty it won't be covered.

The car always had the official VW service done at the proper intervals
at a VW dealer so I'm pretty sure the ecu was flashed long ago.  
Especially since it had cold start problems back when it was new.  
Unless you are referring to a more recent flash.

I agree that MIL light problems warrant a visit to a competent VW
mechanic.

Thanks,

Bill

coil over plug coils, thus can't see secondary voltage.