Ahhh it is starting to make sense now Matt.
1131 and 1151 are lambda sensor issues the latter usually relating to cylinders 3/4 and the first code for cylinders 1/2 all running lean...
It would be normal to assume that both lambda sensors are on there way out, but it is extremely unlikely that both would actually start to fail at the same time, they are in two separate catalytic converters for a start.
So it is a case of them reporting that the engine is running lean and not the case that these two lambda sensors at actually at fault.
So... We have to look at other options here... If there is a fellow forum member who lives in your area with a jts it may be worth while swapping maf housings over then checking the codes on both cars, see if the codes clear then you have your answer.... This will confirm if the maf is bordering on failure which indeed, I have a sneaky suspicion it may well be.
As for the lumpy misfire when cold, it could be related but what is concerning me and throwing a swerve ball is the lack of natural pressure present in the fuel tank and system either when hot or indeed, cold. There should at least be some present thus the hiss I was referring too.
If the system is taking its time to reach pressure initially then the injectors and sensors will run lean anyway and given the jts is a renowned sensitive beast of an engine, it's fair to assume that because of a lean, lower pressure one cylinder, usually number 4 is going to initially starve of fuel until that pressure builds up via the fuel pump in the tank and the high pressure pump in the engine bay....
The question is, why isn't the system maintaining pressure initially after standing?
Fuel filler cap seal, possible!
Fuel filler neck and clips leaking or split, possible!
Fuel pump in the tank getting lazy, unlikely!
Broken seal on the top of the fuel pump sender housing, likely but would be associated with a smell of petrol conning from under the rear bench seat.
High pressure pump, probable as they are a known factor to get lazy and fail eventually , bear in mind that a twin spark doesn't have one but the jts does.
So.. plenty to talk over with your specialist and many things you can pre- eliminate yourself before hand.
The injectors in your car are a known issue but in this case, I personally think it is a red herring to assume that they are the cause... An injector will run bad or run well but it won't do it intermittently. Once they block or fail, they stay that way until rectified or changed....
Given the fact that they have been given a recent terraclean treatment this becomes even less remote that they are causing the issue... They can only perform the job of regulating a spray at a given amount and time frame dictated to them via pressure and regulated from the ecu sensor readings.
So to recap.
Try a different maf housing, and get the fuel pressure from the filler cap onwards to the HP pump tested for air leaks, these are the most likely and logical sources for both of your issues
If your specialist is at a loss how to check a fuel tank and filler neck for leaks short of stripping it all down
suggest an air hose and a rubber bung for the filler neck.. build up pressure to 30psi and listen for any hisses from the filler neck, tank or indeed the top seal. A trick I learned in my main dealer technician years
Ps... Look for my posts on safety feature on the q system referring to cleaning a brake light switch... Same principle on all variants, It could be that simple with regards to the circuit