I have a '92 3.1l firebird with a surging idle and really bad mileage, and Im going to do a vacuum test this weekend.
Where on the vacuum system do I attach the vacuum gauge?
And will it tell me the overall condition of the vacuum system, including all the vacuum hoses and the brake booster? or just the manifold vacuum?

All answers is appreciated. Thanks.

 

Hook it up to the the t-line at the back of the intake manifold.

 

Where at the T-line? The one that goes to the brake booster or the other one? Does it even matter? And will it tell me the overall condition of all the vacuum hoses o do I just get the manifold vacuum?

 

It will tell you manifold vacuum + the seal of all other vacuum lines attached minus the one you unplugged, which I imagine is what you want. Try it from the other port if you want. If you see any lines you suspect, a good way to test is to unplug the whole line and plug one end while sucking the other end. If it collapses, or you can suck air while its plugged, that line is bad. Even if a line just looks dry or cracked or suspect you should probably chane anyway. Try some carb cleaner around intake gasket surfaces and areas where there could be a vacuum leak. If you see a jump in idle, the motor smooths out, or you see vacuum increase, you probably just found a leak. Just be careful with the spray, dont spray it on your exhaust or empty the can on your motor.