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The powertrain control module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open Loop and Closed Loop. During Open Loop, the PCM determines fuel delivery based on sensor signals, without oxygen sensor (O2S) input. During Closed Loop, the PCM adds oxygen sensor inputs to calculate the short and long term fuel trim, fuel delivery adjustments. If the oxygen sensors indicate a lean condition, the fuel trim values will be above 0 percent. If the oxygen sensors indicate a rich condition, the fuel trim values will be below 0 percent. The short term fuel trim values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. The long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. If the PCM detects an excessively lean condition, diagnostic trouble code (DTC) P0171 sets.
Your problem is very likely to be a leaking intake manifold gasket.
HOW WOULD THIS BE CONFIRMED? WOULD THE TEST BE COSTLY? AND IF IT
WAS CONFIRMED TO BE A LEAKING INTAKE GASKET, IS IT A COSTLY REPAIR?
It is a 2.0 labor hour job & 65.00 parts if plactic upper intake is ok,if not add 100.00
These intakes are bad about burning thru at the EGR valve. Using a spray can of carb spray (spraying in short bursts) around intake & watch 0/2 sensor,if voltage stays above .875 MV ,you found the leak.