i recently encountered with boost leaks with a car i tuned.
the map sensor reading were stable, but, a faulty idle speed valve was sending the boost through.
that car was poorly built and didint recycle it's ISV into it's intercooler piping.
the map sensor read about 3 psi of boost, also the other mechanical gauges attached to the vaccum hose junction
read the same. i have replaced that valve and got a new boost reading so i understand it's malfunction.
the thing is, how can it be detected, without pressure testing the boost pipes?