Help! False codes?!

[KeithSam]

Advice needed.
My 2004 A4 3.0L throws CHECK ENGINE codes every 7-10 days, PO 300 and PO 304 or 305, misfire in cylinders 3, 4, or 5, or various.
However, we have replaced:
all the ignition coils,
all coil clips,
fuel filter,
plugs,
battery,
alternator,
PCV VALVE
the car runs 100%, no funny idle, no missing, etc.

A shop owner said it may be a vacuum leak but we have yet to find one.
That said, I get alot of false warnings from this car, could this be another one, or .perhaps a subtle problem we are not thinking of?
(My power steering pump just died)

Car runs fine otherwise.

Advice?

[diagnosticator]

The ECU detects misfires differently than you do. Specifically, the ECU monitors the crankshaft speed/position sensor output frequency, and infers the angular crankshaft velocity from the sensor output voltage frequency. Misfires are detected when the instantaneous angular velocity of the crankshaft dips at some angular sector of the full circle, and depending on what angular sector the dip in velocity occurs at, determines what cylinder is not contributing it's share of the torque compared to the other cylinders. The dip in angular velocity is inferred as a misfire. The misfire recognition in the ECU includes filters to remove noise from the crankshaft speed sensor input to the ECU, and filters out certain frequencies and harmonics that are known to be from non misfire sources. Anything in the drive line that can effect the crankshaft angular velocity over a similar time period, could be misinterpreted as a misfire. One possible source that could be involved are loose driveline parts. Of course, it is most likely partial misfires are actually occurring, but you don't notice them. Partial misfires are usually associated with lean air/fuel ratios, or faulty ignition.

[KeithSam]

Wow!