To be certain, you should:
* Consult your owner's manual: This is the best resource for the exact location for your specific Cavalier model and engine.
* Look at a diagram: A Haynes or Chilton repair manual for your year and model will have a detailed diagram showing the location. You can often find these online.
* Search online: A Google image search for "1990 Chevrolet Cavalier PCV valve location" along with your specific engine size might yield helpful images.
Remember to be careful when working near the engine compartment. The engine may be hot, and there are other parts that you could accidentally damage.