29F4 Cat Sensor HELLLLPPPPP

[JakubJames]

Hi all,
I know this topic has been brought up excessively in the past but I literally cannot seem to find a complete resolution.
I have a 2008 BMW Z4 2.0 E85 (83k miles) and have had the EML light on for some time now. The error code is 29F4. I've tried adding redex, running premium petrol etc and then resetting the code but it always comes back after a day or two.
The car runs fine except that sometimes when I take off from first starting the car or at traffic lights it judders. I'm not 100% certain this is related.
My first port of call is to look at changing the cat sensors. I recently had an MOT and the emission levels were fine so I'm thinking it's a sensor issue rather than a cat issue. I'm thinking of changing the post cat first, would this be a wide course of action? I bought a pre-cat sensor by accident so I will probably put this on at the same time.
Please don't link forum posts where no solution is advised or resolved.

[ph001]

The reason you can’t find a complete resolution is probably because nobody has ever really pinned down the problem short of changing the whole exhaust system, manifold and lambda sensors included. Some people have had some improvements simply by changing to a different fuel although even that seems to be temporary.

I suspect the majority are suffering from cracked manifolds (whether they realise it or not) so that is where I would start. Can usually be welded up for a lot less money than new (cat is part of manifold unfortunately).