1999 Land Rover Freelander lambda sensor

Engine Mechanical problem
1999 Land Rover Freelander 4 cyl 1.8 petrol Manual

hi all, I have recently bought a landrover freelander, it had been sitting still for approx 12months so once I had it in my grasp I immediatly gave it a good service, new brakes, new air filter, sparkys, oil filter, oil, water ect ect.

but no a few months down the road, I have the nasty smell of overfueling, bad emissions, a rattly cat that is blowing and alot of what I can only describe as 'clutch judder' and cut out of the engine now and then.

am I right in my assumption that the lambda senser had faulted, meaning my emisions had corroded my cat. And the cut out are from the unbalanced fuel mixture in the system?

also I have bought a new cat, which I will be replacing tomorow, along with a new Lambda, however iv had a nose and cant see a way of getting to the sensor in the manifold, can anyone give me tips on a easy way of reaching it?

all help is very much appriciated.