I'm stumped,... but I'm guessing that the injectors would give a much higher pitch sound,.. more of a click or ticking not a deeper knock sound. Can you get someone to work the throttle while you try to locate the source of the noise, or do you have to drive it to get the sound ?? What about disconnecting that vacuum line again to see if it stops the sound,... it probably won't run worth a crap but it might help zero in on the source of the sound ??