Prius Gen 2 stumbling, cold start rattle, running lean? Blistered spark plugs, pinging when hot

I have an issue that seems to be getting worse and has gotten annoyingly worse after new plugs and throttle body clean.

Has always seemed to ping a little under load when at operating temp and slight/moderate acceleration. Didn't think much due to many other cars doing the same.

Then started to rattle on cold start, stumble/shake.

Recently changed plugs and cleaned throttle body a little (in situ). Old plugs all blistered. Cleaned pcv valve. Seemed to move ok?

Engine start shake seems a little harder, and it's revving high when coasting down or low speed idle, slowly coming down at complete stop.

I did a battery D/C.

No codes from my OBD2 Bluetooth. It's old but has shown a misfire before when there was a tiny bit of moisture in one cylinder.

Any thoughts or other things to check? I guess I could clean the maf though it didn't seem very dirty looking at the temp "football" thing in there

 

NGK Iridium Spark Plug - IFR5T11 from local auto parts shop

 

The symptoms appeared on the old plugs after running fine.

From my reading, people change all sorts of things, and it doesn't necessarily fix the problem.

Has anyone had all the problems listed above, simply from branded "fake" plugs?

 

I have the Torque app, not sure where fuel trim would be shown?

No dashboard lights

 

I cleaned the maf sensor, found it had oily black on all the bits I couldn't see from the pre-throttle body tube.

Seems to be running better now. No pinging, no stumbling, much softer engine engagements. We'll see if it re-learns the pinging behaviour or not.
I also put premium fuel in before, to maybe make it slightly easier while this problem was occurring.

I guess oil build up is normal over time, though I recall once slightly over filling.
I'd also used a different oil brand with a 5w-30 "long life engine".
Not sure if that would have any effect. Usually the car has 5w-40 . Any chance of more oil vapour with the thinner hot weight?