Turn the ignition switch on and observe the light. Short out the A and B terminals on the ALDL and observe the flashing light. Write down all stored codes and send them to me for further analysis if you don't have the service manual. Vacuum hoses for splits, kinks and proper connections as shown on the Vehicle Emission Control Information label. Ignition wires for hardness, cracking and proper connection at both distributor cap and spark plugs.
Check throttle linkage for sticking or binding.
Check carburetor for flooding - look down the throat and see if there is gasoline flowing from internal seams or jets. Check the engine idle speed, both base and ECM controlled. See the vehicle Emission Control Information label. Check the EGR operation - there should be NO EGR at idle. You may have to remove the EGR Valve to inspect the internal valve.