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I Googled "smoke machine" or "vacuum leak" and did the one on Youtube using a one gallon paint can. Two 3/8 holes drilled in the lid, attached a couple air hose fittings that came with my compressor tools. One connects to the compressor, the other to a washing machine fresh water hose (smaller diameter than a garden hose). Jam the other end somewhere in the intake. Not the J pipe because that's a likely source of a vacuum leak. Do this all with the engine off, and cold, as warm engine parts can expand enough to close off the leak you're trying to find.
If I had to do it again, I would remove the MAF which you have to do any way to keep it from getting contaminated, and shove some rags in there to keep the pressure from coming back out the air filter. But I'd attach the smoke end of the hose to the manifold. My best idea is to use the rear-facing port on the top of the manifold behind the passenger (US) seat. It's the part that's used on the opposite manifold to connect to the brake booster.
Then put some mineral oil on some rags and light them, wait a few seconds and stomp out the flame. Drop the smoking rags in the can and hammer the lid closed. Tough to close completely if there's a lot of old paint on the lid but do your best. Have someone turn your compressor on for a few seconds at a time, or rig up an in-line valve, or use an electric tire inflator to generate some low but steady pressure, I think a couple PSI is enough. Fresh air being pumped in will keep the smoky rags going, but mine went out a few times. Then look for smoke coming out of the motor, and have a flashlight handy.
Apparently you can use the same thing to locate exhaust leaks.
You're looking for air that cheats its way in after the MAF, so maybe prop the throttle body open to make sure the smoke can get to the resonator and rest of the intake before the TB, maybe there's a leak there.
But don't take my word for it, I did all this and did not find the leak but may get back in there depending on how my fuel trims look later on.
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