Idel speed problem

Irregular idle speed in cherokee 1989 4wd, when starts go to 2000 rpm, then to 300, 3 or 4 minutes later to 1000, back to 300 and go to 1500.
I just check the tps voltaje and it´s ok, install a new IAC valve and the problem presist, I already check all the vacummlines and change with new vacumm hoses. Check and install new gasket in exhaust and main, check for vaccum leaks and all it´s ok
please help me this is drive me creazy.