i have an exhaust leak and i was wondering if that would cause the oxy sensor to pick up its running lean and just keep adding petrol to the point where i can smell the fuel. when i turn off the car it wont start until it sits for a while. i have also noticed the idle and the above problem have gotten worse as the exhaust leak has gotten worse.

only if the leak is between the sensor and engine, eg exhaust manifold to head..
but it wont get that rich where it wont start..

+1
Must be another underlying issue.

its the factory manifold and its a bad leak too. what i was wondering as ive seen it done before. could i get exhaust and muffler putty fill the gap all up around the entire gasket cut abit of coke can or something put round it then hose clamp it down until wendsday could that fix the problem? i have extractors and a cat to get fitted after wendsday.

There's a lot of pressure in the port when the exhaust valve opens. Trying to seal around the outside is a waste of time - it will just blow out. Bite the bullet and replace the gasket. A gasket is not expensive, and it doesn't take long to replace. You may even be lucky and able to re-use it when you get the headers put on. Just spray the manifold nuts liberally with WD40, CRC 556 or similar several hours before or preferably overnight, to loosen the rust. And clean the head and manifold joining surfaces thoroughly so the gasket can seal.

If the O2 sensor reading lean is causing your issues, you can work around that. Disconnect the sensor and leave it that way. Disconnect your ECU (behind passenger footwell kick panel) for one minute to clear the fuel trims, then reconnect. With no O2 sensor input, the ECU can never go into closed loop, and will operate solely off the fuel tables - just like it does when accelerating, when cold, on overrun, etc. Unless the tables are super rich or super lean, running like that for a week won't cause any issues. Running without O2 feedback long-term can damage your cat (clogging or overheating) if the fuelling is way wrong. But, if the problem is a manifold leak, you are introducing cool air, so your cat will be fine. I have no cat (legal here), and have run without O2 feedback successfully for months. Incidentally, if disconnecting the O2 sensor as above doesn't fix your problem, then the sensor or a leak ahead of it is not the source and you need to look elsewhere.

Okay ill look into it.