92 305 idle issue sometimes high then goes down once in blue moon low a/c affects its if I turn on idle drops doesent appear to be vac leak new Idle air put in im aimong for just doing a tune up having timing checked ideas? Stock 305 tbi 92 rs

 

Do you have any exhaust leaks? Mine had the same issue, and the exhaust had leaks. Repaired the leaks and the idle smoothed out.