Help! I have a wideband lambda fitted to monitor fuelling, last few weeks it is showing lean numbers, as follows:
Start in the morning it's 14.5, stays like that on warm up.
After a few minutes/miles it drifts to 15.8, it's 20/21 on the overrun, and I'm too afraid to hit boost.
It used be lower all over.

And it's not the gauge is wrong, as its popping much worse on the overrun, and won't idle after a few minutes, I've to give it throttle to stay running.

It's running standard boost, Unmodified except front mount and exhaust.
I tried a different TPS but to no effect and I don't think it's a boost hose leak.

Any ideas? Starting with the cheaper fixes!