Uneven at idle and low revs

[DrRobin]

Sorry for the long post, I hope all of the detail points towards the real problem as I feel I have been skirting round the issue. 2001 986 2.7L with 93k miles

This has been on-going for a couple of months now and I have been through a few things as follows:

- Serviced at my local indy as normal in May. The water pump went when the garage reved the engine to get it through emissions. No other problems.

- Over-heated in a traffic jam in middle of a hot June day. Turned out to be an old expansion tank filler cap, replaced and no further problems.

- Late June, noticed there was something blowing from the exhaust, tracked it down to a hole in one of the CATs.

- Early August, New CATs fitted at local indy, ran okay away from the garage, but a couple of days later I got O2 age codes on all four O2 sensors and then later a misfire. To be fair some of the O2 codes might have already been there as my code reader didn't identify the post CAT codes.

- New O2 sensors obtained and fitted, late August by me. They took ages to arrive and I could only get generic Bosch sensors (correct sensor), so spliced them in to the original connectors using the crimp connectors which came with them. O2 codes gone, but I still getting a random misfire.

O2 outputs look fine, pre-CAT move up and down, post CAT fairly stable.

- Sept, random misfire continued until I realised the battery was very low, charged up and no misfire. My CTEK battery sense said the battery went down to 8V whilst the garage were changing the CATs, I guess they left the key in the ignition over-night and drained the battery.

- Also cleared the ECU.

- Sept/Oct, no misfire recorded but uneven at idle and low throttle openings. Cleaned throttle body, small improvement.
Removed oil cap, ran very rough.
Checked coils, all six had a small crack, so replaced all 6 with Beru.
Plugs looked okay, may be slightly rich/unburnt fuel, but replaced.

- Oct, Long term fuel trims have settle down to about -4% on bank 1 and -5% on bank 2. Short term fuel trims look fine.

- Nov, uneven running at idle and low revs continues. I have just bought a new air filter as the old is okay, but a bit old. I will also have a look at and clean the MAF sensor.

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This all started when the CATs were changed, I didn't notice any problem before. The O2 sensors were probably on the way out before the CATs were changed and in hindsight probably should have been changed with the CAT as swapping them over finished them off.

If it turns out not to be the air filter or MAF then I suspect the O2 sensors, even though the graphs from them look fine.

Could O2 sensors cause uneven running?
Is there anything else I should check?

Ta