I have a stock 89 camaro rs with the 305 and when i start it up, the idle speed fluctuates from 500 to 1700rpm. it does this for about 2 minutes and then it levels out at about 1200 rpm. I replaced the O2 sensor, EGR valve, spark plugs, wires, cap, rotor, coolant temp sensor, thermostat, rad cap, a ripped vacuum line, and air filter. Any ideas on what could be causing this issue?

 

id say there is a vaccum leak sumwhere still. CAUTIOUSLY with engine running, try spraing litely in mists carb cleaner or starter fluid around intake area n see if ur motor idles higher any.