I am suprised that you did not mention the PCV valve - and that you let the air filter go 30k.
The CEL does not have to be on, there may be codes stored anyway.
Vacuum leaks are often the cause of this kind of problem. Check the valve and hose which are under the throttle body.
I assume that you do not know if it's running too rich or to lean.
A computer diagnostic will tell you if a sensor is bad, or point to the problem if it's mechanical.
