Help needed with fault diagnosis - Fault Codes supplied

[Tingtong]

Hi everyone, just found this site and it seems excellent, thought I would write to try and glean some technical information from some of you..

First of all, it's for a 2006 VW Polo 1.2 - It has recently reached 70,000 miles

I have recently purchased a snap on microscan to troubleshoot my Engine management light and it came up with a few codes, they were the following:-

16804 (P0420) - Catalyst system bank 1 operation below threshold - intermittent

16556 (P0172) - Fuel trim bank 1 system too rich

16556 (P0172) - Fuel trim bank 1 system too rich - intermittent

16685 (P0301) - Cylinder 1 misfire detected - Intermittent

16686 (P0302) - Cylinder 2 misfire detected - Intermittent

16687 (P0303) - Cylinder 3 misfire detected - Intermittent

16684 (P0300) - Random/Multiple cylinder misfire detected - Intermittent

Now I have replaced the individual coil packs and spark plugs and it seems to be running a little bit smoother, but it is not very stable at idle, it seems to struggle when the air con is on and nearly stalls. Is there anything that is common to all of these faults at all..

Just to let you know, I have cleared the codes now and they haven't reappeared in 50 miles or so...

Any help would be much appreciated.