i think ur rpm problem has something with fuel/ignition. i may not be as knowledgable as others on this forum but sometimes simple thinking is the way to go
these are something i think may be wrong.
worn spark plugs/ incorrect gap
low fuel pressure (messed fuel pump)
or maybe something with the MAF
agian, as mentioned previously, its hard to diagnose over the interent, ur best bet if u have checked/replaced all these things is to take it to a shop.