Quote Originally Posted by 99GT2dr View Post
That exhaust leak is absolutely your primary concern. Trying to figure out how to help you understand why.

Let's say you're driving down a road blindfolded that you're really familiar with, you kinda know where the curves and what not are by memory (open loop) so you're able to drive along ok, not perfect but good enough.

Now let's say instead of using your memory, you're going only by what your crazy ex-gf that hates your guts is telling you to do in the passenger seat (closed loop, 02 sensor not getting proper readings due to xover not bolted on).

The VE table in the pcm has a pretty good idea of how much fuel the engine needs to run at a given map value (which is what it does when you unplug your maf), so it just gives it that much fuel. As opposed to listening to the crazy ex (02 sensor adjusting fueling with bad data because huge exhaust leak).
I don't know you; but this analogy wins.