I'm not real familiar with the four banger TBI, but I'm guessing it's fairly generic. I use a piece of paper towel or something white, and hold it on the bottom end of the sprayer noozle (injector). You can see if it's wet, you can also often smell fuel. The TB will generally hold pressure (when the motor is off), it will deffinately pressure up with the key on (at least for a few seconds) and then supply constant pressure when it's running.
I was thinking, it's also possible the inside of your intake is dirty enough to soak up some fuel.
Motors typically have a coating of carbon in the crown of the head, on the valves and/or on the top of the piston, that can hold a spark for awhile. As long as the motor is still getting fuel, from a leaky injector (TB), fumes from the intake or possibly out of the charcoal canister, it can diesel for while. Pretty common with carburated motors.
You may have to jump the fuel pump, to a hot wire, so it is constant on (without the motor running). It may leak down rather quickly and it may be hard to spot the leaky injector. The pressure may leak off, faster than you can test for a little extra fuel dripping out after the motor is stopped. Or you may need somebody to turn the key on and off a few times, to get the fuel pump to cycle for a few seconds (typical prime cycle), to keep enough pressure on to test for a seep.
A 1000 RPM seems a little high (most motors are set between 600 and 750). But not really high enough for a serious vacuum leak. I'd unhook the purge line from the charcoal canister to the intake manifold and plug it, just as a test.