92 GMC 1500
My truck won't stay running unless I'm
pressing gas. It won't start. Got new fuel
pump cleaned filter what could it be. I lost
gas cap could that do it
Without a gas cap I'm surprised it doesn't have the check engine light on. Get a gas cap on from junk yard or parts store. If you cannot pass emissions, spray a pinch w d 40 under gas cap and put back on. Hope it helps.
A missing gas cap won't keep the engine from starting or cause your problems. Most likely, this is a dirty idle air control valve or defective cold-start injector sticking at startup, and opening up using the accelerator makes up for this. This also affects how the engine behaves when coming to a stop. This could also involve the throttle position sensor and/or the fuel pressure regulator.