Question about 1999 Chevrolet Silverado 2500
Good details. Backfiring through the carb suggests a leak in the air intake manifold. Check all vacuum connections. If all OK I would check three things 1) Idle Air Control valve (IAC) on the throttle, If clogged just clean it out with carb cleaning fluid. The IAC is controlled by the ECU to bleed a constantly regulated amount of air around the closed throttle at idle, this is the other half of the TPS system 2) Throttle Position Sensor (TPS) - but you have already changed it and 3) Exhaust Gas Recovery (EGR) valve. From what you describe I put money on this last one - sounds like its jammed open. The device is usually under the air cleaner and looks like a flying saucer about 3 inches in diameter. It has a narrow diameter vacuum hose attached to an arm on the top. The purpose of the thing is to introduce a little exhaust into the air intake to cool the fuel ignition temperature in the cylinders and thereby eliminate nitrous oxide in the exhaust. Exhaust gas sits one side of the valve and when a vacuum acts, through the small diameter pipe from the inlet manifold, it draws up the EGR diaphragm to open the valve. Remove the EGR and give this a thorough clean (encrusted carbon deposits - carb. cleaning spray) until you can see that applying suction to the vacuum connection allows the valve to move freely. Whilst the EGR is off check the exhaust feed pipe and make sure it is clean. If not a bit of frayed brake cable makes for a good internal brush to remove clag. Hope that these hints do the trick
Posted on May 01, 2010
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Posted on May 01, 2010
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Posted on Jan 02, 2017
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