Hi all,

Looking for some advice. Sorry about the lengthy post but wanted to give all the info i have.
We bought the A6 at an auction about 3 months ago so have no service history.
So, to get started here is the car info:
2002 A6 Quattro 3.0 V6 Auto
158,000 miles (250,000km)

Background:
A couple of months ago CEL came on with Cyl 2 misfire and there was a slight misfire noticeable.. Replaced the coil pack and all was well.
CEL came on a couple of weeks ago - code P0431 warm up catalyst bank 2 efficiency below threshhold. I should point out the car was running great. I cleared that code.
In the meantime I changed all the plugs with iridium tipped ones. Also changed air filter.
The CEL came on again a week later - P0431. Again, I cleared the code. I figured now I got to fix this and have started to do some research even though it is still running great.
So yesterday my son had the car (I was not there). He started it - apparently a bit difficult to start. As he pulled out of the parking lot it started mis-firing very badly, no power and the CEL flashing. He stopped and shut the car off. He restarted it and it ran fine. Would never know it acted up except the CEL is back on (not flashing). I drove the car to work today (40 miles round trip) and it ran fine except for the last mile where the engine was no longer idling smooth. In the garage, in park, at a very light throttle the RPMs osilate between 800 and 1000. At heavier throttle it seems smooth (this is a new symptom).

These are the codes it threw:
16684 P0300 Randome multiple cylinder mis-fire
16689 P0305 cylinder 5 mis-fire
16688 P0304 cylinder 4 mis-fire
16687 P0303 cylinder 3 mis-fire
16685 P0301 cylinder 1 mis-fire

So, only cylinder 2 did not throw a code - the one with a new coil pack.
After that long winded description - looking for suggestions. Can 5 coil packs go? Is it somehow related to the P0431 code? Hoping I can get some suggestions with all the experience on this forum.

Thank you.