Check to see if there is adequate vacuum from the manifold port and carb ports. It could be a bad IAC sensor (about 40 bucks) or a clogged catalytic converter (about 175.00) or muffler (about 45 bucks). If you notice back pressure instead of vacuum on the ports it is likely the muffler or cat converter. Of course all of the sensors will be off if you have excessive back pressure. Another tell tell sign is excessive oil leakage from valve cover gaskets, rear main seal, and excessive build-up in the carb.