I can't quite comprehend the sound of a vacuum hose popping off. The sound I would expect would be a hissing with the engine running, but if it won't start, you would not get that either. Can you describe the sound better?

I would pull the air cleaner (three nuts) and have someone observe the airflow meter vane while trying to start. It should deflect a bit from rest. If it does not, you will get no output flow from the injectors because the fuel distributor will keep the secondary pressure below the cutoff pressure of the valves in the injector inlets. If the plate does not deflect, you may have a very major vacuum leak. If it DOES deflect, your primary fuel pressure may be too low.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7