Assuming a 14b turbo, a 2" hardware store rubber coupler(with worm clamps), and a 2" PVC cap, a 16G has a tad larger opening, but small enough to squeeze a 2" coupler. Either buy a cap with a 3/8" threaded hole and put a quick connect NPT air fitting(threads are compatible) or just a tire cap fitting by pre-drilling a hole. Essentially you just want to put a cap over the turbo inlet and seal it. Then using compressed air, pressurize no more than 20 to 25 psi(no more than slightly higher than you would under boost) and check for escaping air. I recommend you rotate your engine to TDC to close your valves.
You will likely hear either a little bit or a lot of air escaping. Track down the source or sources by sound, feel, or soap bubbles. Take one leak at a time from easiest or largest. Come research whenever you think you found one that might require a complex part to be disassembled. Some leaks are easy to fix, some are not worth the effort if they are small leaks. Some air will escape. A turbo is not perfectly sealed. You want to get the most obvious. Keep the leaks far under the ability of the air to compress while in boost. The ECU will be able to perform better because the volume of metered air in the system remains the same. If your engine is erratic or lacking in power that is one of the first things you should check.
