Q: p0171 and p0174 /p0104 on 1996 Chevrolet 1500 Pickup

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I have a problems when I start the the truck sometimes runs fast and sometimes stall when I put it gear or when I make a stop I replace the mass flow sensor the idle air control valve and the thottle possion sensor and the problem continue I would like your Help thank you.
(1) Answer
Your symptoms sound like a classic vacuum leak or unmetered air leak (broken air box/tube/etc...). Check for disconnected hoses first. After that, if no luck, you will need to enrich the air with a fuel (propane, for example...) around various areas in the throttle body/intake manifold area to see if the running condition improves, and where that occurs. This is probably something less likely for the do-it-yourself mechanic to perform.

Good luck!
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