Rough Idle/lean help?

[Martinw2579]

So last night while outside my mom's house, I noticed that my car was running lean @ around 15.8ish and higher (norm is 14.8) and then it started doing a rough idle. Then on my way home, if I gave it about like 40% throttle, it would like cough cough as if my IC pipe came off or w/e. Got it home, oil was right under the "L" mark and I topped it off. This morning I go to turn it on and same thing...rough idle. S14 Sr20det motor, fmic, full exhaust, truboost, wideband. The owner before me effed up one of the spark plugs threads and put a bigger one for a 5.0 mustang in it and it just "sits" in there but a little snug and I haven't checked to see if thats the issue yet but yeah....Any thoughts or money tree that anyone wants to give me?