High idle

I have a 91 toyota camry with a 2.5 it has about 146000 on it I have done all I can to fix the problem but I still cant figure it out I put in a ecm, iac, tps, temp snsr comp tune up, upper intake gasket, mass air, somekind of vac snsr on the rear valve cover, the problem is it idles at 2500 to 3500 and stays there but sometimes if I shut it off and start it several times it will be just fine idling at 700 rpm and then other times it wont do anything wrong by the way if your help is correct I will make a deceint donation

thank you for your time

Michael