Code P0171, rough idle, shuts off at stoplights?

2000 NISSAN ALTIMA
80,000 MILES • 2.4L • 4 CYL • 2WD • AUTOMATIC
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MTBOR
  • MEMBER
  • 1 POST
Replaced MAF with a Denso unit, did not correct the problem. Cleaned the throttle body with throttle body cleaner and a plastic brush, no change.

Hooked a smoke machine to the brake booster line and got some puzzling results. First there was a pinhole in the intake resonator (black plastic reservoir under breather tube), since this is post MAF this definitely needs corrected.

What I am unsure of is why there was smoke literally pouring out of the EGR regulator as well as some smoke coming from the bottom of the EGR itself (through the ports). I'm unsure if there is something specific needed on this car to either route around the EGR, or force it closed prior to doing the smoke test. It seems unlikely that both of those components are faulty. Seems like it should be naturally closed. Smoke test was performed without any circuits energized.

Another curious thing about this vehicle is that it puffs air rather forcefully from the oil fill if the oil fill cap is removed. I haven't done a PCV valve because they're quite difficult to get to on this vehicle... Could this forceful air be making its way into the intake and causing a lean condition?
Mar 21, 2024 at 5:46 PM
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JACOBANDNICKOLAS
  • Experienced Mechanic
  • 110,240 POSTS
Hi,

You should actually feel a slight vacuum when you remove the oil fill cap. It's possible the PCV is stuck closed or plugged.

As far as the code is concerned, it does indicate a lean condition. In addition to a vacuum leak, it could be related to an injector issue, low fuel pressure, an exhaust leak, a leak at the intake gasket, and so on.

Take a look through this link. It explains how to check for a vacuum leak using a carburetor cleaner. Try this and let me know what you find.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know.

Joe
Mar 22, 2024 at 2:42 PM
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