When you come off throttle, we have all seen our boost guages drop below the 0 mark, this is then into a negative boost pressure and will cause air to be drawn in through the place where there is an air leak.

This then causes the MAP sensor to see more air than normal so it puts a smidgen more fuel in to compensate, thus overfuelling, this passes straight out of the exhasut manifold as unburnt fuel and ignites with the temperatures of the exhaust, thus causing flames out of the exhaust.

The lean side of things is because when on boost the map sensor doesnt see 100% of the boost created by the turbo, which it was mapped for, as air is passing out the leak, thus causes it to underfuel for that reason.


I think thats right.........................