lol no wonder so many good engines get blown up, aem widebands are only £128 from usa.
if you cant afford or refuse to buy a wideband then leave the car standard its as simple as that, things go wrong sometimes through age/wear let alone messing with it and not knowing what the hell ur doing !
its honestly a recipe for disaster, either do lots of research and get some monitoring equipment or get it to a good reputable tuner who has experience with mfi rs turbos.