Check Engine light on, won't go over 6k rpms

So I started having this problem about a week ago. I let my car start to warm up for 10-15 minutes, half the time if works fine, the other half it slowly goes to 6k rpms and tops out there. I've fixed it by jacking the car up on the left side and lowering back down and it will do fine. It has become more and more of a nuisance as of yesterday. Any idea what's wrong with my baby?? Thanks guys