Looking for fuel shut off switch in 1996 oldsmobile ninety-eight

Possible faulty crank sensor or idle speed controller, fuel pump relay, or ignition module. Get a data scan and see what's sensor might out of range or defective. Check for clogged fuel filter also.

Yes it can

needs a fuel system flush

make sure you have as little gas in the tank as possible, unplug tank , usually up near top or tank if possible , unhook gas fill tube from fuel door area , (screws usually inside fuel door), unhook fuel lines from tank closest to the tank as possible, place jack under fuel tank and slightly tighten to tank, release tank straps and lower jack, roll out free from under vehicle and remove pump from tank, reverse process to reassemble.

Its on the passenger side of the heat duct mounted with 2 screws

relay is under the hood, i would try to replace the switch first....

low fuel pressure or none

I would say try changing the spark plugs and spark plug wires if gas is old put in at least 5 gallons of fresh gas and change the fuel filter.

Check egr valve, check pvc valve, check head gasket, check air filter, timing timing out of adjustment, burned valves or leaking, cam shafts could be worn, check fuel enjectors.