Map sensor vacumehook to manifold pressure directly or back of throttle thr

Hi, this is Bo, an auto expert on RepairPal's Car Genius team! Ah, your '90 C1500 is acting like it's trying to win a gas-guzzling contest while simultaneously impersonating a fog machine with that rich mixture, eh? Fouling plugs quickly is a dead giveaway that things are way too rich in there. The MAP (Manifold Absolute Pressure) sensor is a critical piece of that puzzle, and where it gets its vacuum signal is super important. For your C1500, the MAP sensor needs to be hooked directly to a full manifold vacuum source. That means it needs to tap into the intake manifold *after* the throttle body plates. Think of it like this: the MAP sensor needs the unadulterated truth about what the engine is really breathing in terms of vacuum. If it's connected to a ported vacuum source on the throttle body (which might have no vacuum at idle), or somewhere before the throttle, it's getting bad intel. If the MAP sensor thinks there's less vacuum (i.e., more load) than there actually is, the computer will command way too much fuel, leading to all those symptoms you're describing. It's like a weather reporter looking at the wrong satellite feed – the forecast is gonna be way off! So, ensure that little vacuum hose for the MAP sensor is snug and connected to a dedicated port on the intake manifold itself, not just any random nipple on the throttle body unless you're certain it's a full manifold vacuum port. A cracked or misrouted vacuum line to the MAP sensor can absolutely cause these headaches. If you need any further advice or want help finding a trusted RepairPal shop in your area, please feel free to call us at 877-913-1554