How do you find a vacuum leak?

Im pretty sure my cars got one. (a vacuum leak that is). I had engine codes for my O2 sensor, and I replaced it, but it still gets the same codes. Im told it can be a number of things including a vacuum leak. (I have a suspicion that it may be something ford did to my car so I would come back to fix my check engine light) For a very long time now, theres a very faint whistle (a low pitched whistle) while driving, and then when I turn the car off, it whistles in a higher pitch for about 1 second. (the pitch escalates during that one second until it stops). Oh yeah... not to mention the bad gas mileage and sluggish acceleration. My big question is, Is there obviously a vacuum leak? and if so, how would somebody with no knowlede of vacuum lines go about fixing this on his own? (that would be me)... thanks in advance.. Rick

Its not too difficult. Chances are its in one of the gasket surfaces, not a hose. Usually the hoses don't leak enough to cause major headaches.

Two things I would do. 1) buy a can of starting fluid (ether). with the car running, shoot short bursts at the gasket mating surfaces; head to manifold, manifold to TB, MAP sensor threads, vacuum port threads, etc. You'll find that if you have a leak, a short burst of ether will cause the idle to rise and/or smooth out.

2) you can use this method on your hoses, too, but it can shorten their life. You could also try other fluids with similar diagnosis success but ether is the only one I know that doesn't hurt catalytic converters. For that reason I suggest you use a long piece of 1/2" ABS or PVC tubing. Put it in your ear and chase around every mile of vacuum hose until your ear hears a hiss, tick, or pop. I've also had so-so luck using sound-killing ear muffs with a piece of 1/4" vacuum line or fuel line stuffed under one ear. Then chase around the lines. The earmuffs block out most of the sound and the only thing that makes it in is the noise coming up the tube.