After getting my oil changed at a local oil change place, my 2002 cavalier started ideling rough, revving up then slowing, stalling on the freeway and my check engine light came on. Any ideas?

Changing oil should not cause any running problems, providing that the oil was put back into the engine and did not leak out. I would check all vacuum lines to make sure that none became disconnected. Check all wiring as well though it's pretty difficult to accidentally disconnect anything. Harness connectors are usually difficult to unplug even when you do that on purpose.If you find nothing unusual, you can have a code scan done free at most larger parts stores. That should give you some idea which sensor may be giving you problems. On GM cars, make sure that the duct work between the air filter and throttle body on the engine is secure. The mass air flow sensor is mid-way between the filter and tb and needs proper air flow in order to operate.
Though the system appears complicated it really isn't but only careful testing can reveal problems. All your sensors work together and when one fails, the computer tries to compensate which causes symptoms that do not always match the problem. The one very necessary item in diagnostics is the use of a scanner and that's one thing I cannot do from here but I hope some of what I said is somewhat helpful to you in understanding what is going on under the hood.