ideling problems

I have a 93 mazda 929. it has over 190.000 miles.that was running perfect before i had a tune up done a few weeks ago.my car idles when i make a complete stop.i took it to 3 mechanics who said the diagnostic test showed no codes.one guy said i had a few vaccum leaks ,in which he fixed.and he cleaned my manifold .but the car still idles.i changed the spark plugs,wires,air/fuel filters.pvc valve,and used gas treatment.i'm at a lost trying to determine the problem.it doesnt do it all the time.and the funny thing is when i take it to the mechanics it runs fine each time.

Try cleaning the idle air control valve.