00 Focus Spudders When Accelerating + CEL

I have a 00 Focus LX, Manual 5spd. I am having problems, when I accelerate (it is worse when the engine is warm than when it is cold, sometimes wont happen if it is cold enough) it sputters. Car has no problems starting, but I have noticed a drop in the fuel economy since this problem started.

The car will sometimes die while idle, usually when it is warm. It will sputter every 5 seconds, unless I rev then the sputtering will stop (when sitting at a light or something, usually doesn't happen).

I have looked through pages of posts on the forum for fixes. One thing I have tried was unplugging the hose from the top of the EGR valve, and plugging it with a screw (Bypassing the system), I know the CEL should come on when this happens, but if it was a problem with the EGR valve or system, the car should have ran fine, but unfortunately this did not fix my problem.

When I took the car to DEQ the Emissions failed (duh), and the code was "System Too Lean".

If it is a vacuum leak, can somone point me in the right direction on how to fix this myself? I have read that the oxygen sensor could be the problem.

Car has 92k on it.

Thanks!