Question about 1999 Chevrolet Silverado 1500

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2002 Silverado code PO174

The service engine soon light on my 2002 Silverado 2wd ext. cab pickup with 5.3L non-flex fuel came on. It throws a PO174 code. I have since replaced the plugs, plug wires, and temperature sensory. The code still came back on. It idles rough periodically, especially when first started when cold. It will drop about 200 - 300 rpm at idle. Do you know what it could be?

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  • kgundi Jan 14, 2009

    2002 Silverado 1500 4.8L 4X4 Rough idle (and stalls) when started cold. Pulled both p0174 and p0171 (System lean, both banks). Fuel pressure good. Checked intake manifold for leaks. Checked for vacuum leaks. Has new plugs/wires and new fuel filter. Haven't checked MAF yet.

  • Anonymous Mar 25, 2014

    2002 gmc sierra 1500 4 x 4 ext cab pickup

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After fighting with mine (2003 GMC 5.3 liter), I believe I have it solved. Mine was throwing P0171 and P0174. Also, there was an occasional p0101. I had a rough idle sometimes right when I started it, but usually after 5 minutes when the fuel system went in to closed loop mode (about 200 RPM swings at idle that slowly went away). Days below 10 degrees were much worse.

I cleaned the MAF sensor, checked fuel pressue, changed spark plugs, and cleaned the throttle body. The code basically means that more fuel is being dumped in by opening the fuel injectors longer. The code is set by the long term trim on the injectors be over 23% (opened 23% longer than they should be based on sensor readings). The extra fuel allows the engine to run with the right air to fuel ratio (not necessarily lean as the code suggests). Causes could be low fuel pressure (from pump, fuel regulator, clogged injectors, and such). Running a scanner on it for several days, everything looked normal.

That is all background. The other cause is that air is being introduced into the intake after the MAF sensor. Extra fuel has to be added for the air that the MAF does not see. I did some digging and found out that the gaskets between the plastic intake manifold and cylinder heads are prone to leaking. I tried to spray throttle body injector around where it might leak to monitor the engine speed, but the air leak seems to be less on warmer days and leaks can occur on the inside edge of the gasket where it is hard to reach with the spray (there are foam ends that open the inside edges to atmosphere). I replaced the gaskets and my long term trim dropped to about 6% from 10% on warmer days to pegged out at 25% on cold days with a cold engine. The work isn't too bad as long as you are patient enough to get the plugs off of the ignitors. I have yet to test it out in cold weather, but I am pretty confident.

Posted on Feb 02, 2009

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When cars/trucks run poor on cold days it sometimes mean there is a vacuum leak on one of the rubber fittings/seals. It would be hard to guess. I would check all the intake places where there are rubber tubes/seals, etc. Look for hard rubber, cracks, or just poor/loose fitting connections

Posted on Feb 02, 2009

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The ECM is thinking that it's running too lean on Bank 2. I think the only problem you have may be the O2 sensor, or Air/Fuel Ratio sensor may be faulty. Sorry, I work on imports. And we use an Air/Fuel ration sensor.

Posted on Jan 07, 2009

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Whether it's a 1999 or 2002, the ECM is thinking that it's running too lean on Bank 2. I think the only problem you have may be the O2 sensor, or Air/Fuel Ratio sensor may be faulty. Sorry, I work on imports. And we use an Air/Fuel ration sensor. If you were getting both P0171 & P0174 then I'd have you check the Mass Air Flow Sensor for any residue on the pick-up wire. Have you checked for an air intake leak?

Posted on Jan 06, 2009

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