I read in another forum that to test for a vacuum leak, pull out the oil dipstick. If the idle hesitates, this means you have no leak. But if the idle does not change then you have a leak. Moreover, if it turns out you have a leak and the idle does not hesitate, then your engine has been tuned to the leak (how does one tune the engine to the leak? by leaning out with the AFM adjustment?). I tried this on my '89 525i (M20, euro) and there was no change in idle even after I pulled out the oil dipstick. My idling does not hunt but is a bit rough and my acceleration is poor until I hit around 2200 rpm. I suspect a leak. Any thoughts?

Thanks,
Philip