Please Help! I have a 1998 Chevrolet Cavalier that has a very low idle causing it to shake when idling. I diagnosed it in AutoZone and received the P0507 Code - Idle Control System RPM - Higher Than Expected Check Engine Code. I replaced the Idle Control Valve as recommended by the diagnostic results and my Chevrolet Cavalier still has the low RPM idle issue and also the code P0507. Has anyone experienced this mechanical problem with a 1998 Chevrolet Cavalier? What recommendations do you suggest to repair this mechanical problem?

It has a new fuel pump, new spark plug cables, and new spark plugs.

 

If it's a high mileage car the engine may just be wearing out. Maybe do a compression check. How did the plugs look? Did you change them yourself or did someone else do it. Did they show you the old plugs? Have you confirmed that new plugs were in fact installed?
Maybe pull the valve cover and check for broken valve spring, bent pushrod, etc.
To check the injectors you can put a long screwdriver on each injector and put your ear on the handle and listen to each injector when the car is idling. Any abnormalities will be audible. (Stethoscope if you got one)
Get a code reader and see if all the cylinders are misfiring randomly or if only one cylinder is misfiring.