what problems would i have? over fueling, irregular tick over? I've just put a de-cat on again but tried to make it hug the underside of the car more and me being a tit welded the lambda nut on the side towards the bottom so I've hit it once or twice, going to re-do the downpipe at work tommorow but just wondering if I've got to use a lambda probe as i might just whack a straigh pipe on with no nut if i can.

With no lambda the engine will overfuel yes. Your fuel economy will be shite, I was getting 20-25 mpg before I changed the lambda on my spi, and now get anywhere between 30 on a hard rag to 40 mpg on a gentle run. Part throttle performance will suffer as well, but I think under full throttle the lambda sensor isn't used. Could be wrong.

so really, not a good idea not to have one?

didn't steve-o on here run his gt without the lambda sensor and he didn't have any probs, and still got around 40mpg?

id like to know the answer to this as i think I've broke the lambda all together now

yeah you'll be fine just running it with the lambda unplugged from the electrical connector on the inlet manifold. you're economy will be a little bit worse than normal, but nothing drastic

If you unplug the lambda the ecu will run a basic map, which is like running a safe mode which will use slightly more fuel. The performance will drop too as it's not an optimum map.

cheers hardhitter, are the lalalaumba sensors the same on all mk3s?