Have 85 El Camino that needs smog test. Smog equipment has been removed but has passed in the past, bearly. What can I do to help pass smog in future. Has new plugs, car runs great. Has been seafoamed. Have to install new wires.

run shell V powergas in the tank for 200 miles before the test

Have a 92 mercury with a 1.6L. Roll the windows up and down the idle drops. Let go it evens out. Same with fan motor. Turn it on. Drop then back up. Same with headlights but as you can imagine you need them at night. What could this be? Alternator and battery are tested good.