'05 Tahoe 5.3 / P0171 / Rough Idle / Misses

[Bwaite27]

NP... Here's the torque specs for the intake.

Intake Manifold Bolt Caution: Refer to Fastener Caution. Tighten: Tighten the bolts a first pass in the sequence shown to 5 Nm (44 lb in). Tighten the bolts a final pass in the sequence shown to 10 Nm (89 lb in).

Yup, did that, too. Lol good lookin out

 

[Ibustbravo]

Yup, did that, too. Lol good lookin out

Your code is cleared?

 

[Fless]

I think I'm pickin up what yur puttin down. Wink wink, nudge nudge. Lmao Thank you kindly

If you do it like that and have emissions testing in your area, the evap drive cycle will show as "not run" and it could fail the emissions test.

Check the MAF airflow reading in g/s and see if it tracks with the engine displacement. Has the MAF been cleaned? Have a known good one to substitute?

When stone cold, compare the Intake Air Temp (IAT) or ambient temp and the Engine Coolant Temp (ECT) readings. Also see if they track somewhat as the truck warms up.

Any exhaust leaks on Bank 1?

 

[nonickatall]

I had the same issue on my truck and it was the vent valve, which is located behind the fuel tank. It cost $20 and is swapped in five minutes.

The evap system is used to prevent gases from fuel from escaping into the environment. Of course, gas must be able to escape, because the air has to come out of the tank when the vehicle is refueled. That's why there is the activated carbon canister and the vent valve, which is open, when the vehicle is switched off.
If I now refuel the vehicle, the air can escape into the environment, through the activated carbon canister.
The vent valve closes when the engine is started, and at the same time the purge valve, which is located at the front of the engine, opens. Then these gases are burned. There is a pressure sensor checking if the system is tight. If the vent valve doesn't close, there is no negative pressure in the system and the message comes: "fuel cap open" because that is the most likely cause.

And because you then have a problem with air leakage at the same time, you have a rough idle

 

[Bwaite27]

Your code is cleared?

No. In fact, on Saturday, I plugged my computer back in and it's showing both codes now. 171 is the "system too lean" code, and 455 is the "evap system, large leak" code. I think they're related. I'm thinking the evap leak is big enough that it's letting too much air into the intake and throwing a lean code. I have some investigating to do. I've replaced so much stuff already and checked everything twice. I'm pulling my hair out at this point.

 

[Bwaite27]

If you do it like that and have emissions testing in your area, the evap drive cycle will show as "not run" and it could fail the emissions test.

Check the MAF airflow reading in g/s and see if it tracks with the engine displacement. Has the MAF been cleaned? Have a known good one to substitute?

When stone cold, compare the Intake Air Temp (IAT) or ambient temp and the Engine Coolant Temp (ECT) readings. Also see if they track somewhat as the truck warms up.

Any exhaust leaks on Bank 1?

I checked the IAT & ECT, but only after it was already warm. I'll check it cold later today, thank you! I did clean the MAF, but I don't have a known working one to sub out. And no exhaust leaks.

 

[29tomt]

When I bought my 2003 Tahoe in 2015 and for a while afterwards , it had a little roughness in idle. One day it crak and shutoff immediately and then it finally did crank and I booked it to the shop I use. Prior to that I had cleaned the mass airflow sensor and the throttle valve butterfly and area with the correct spray for each. After putting it on their engine analyzer, shop came back MAF sensor defective. They replaced the sensor. Made a huge difference in idle and overall perf of engine.

 

[nonickatall]

When I bought my 2003 Tahoe in 2015 and for a while afterwards , it had a little roughness in idle. One day it crak and shutoff immediately and then it finally did crank and I booked it to the shop I use. Prior to that I had cleaned the mass airflow sensor and the throttle valve butterfly and area with the correct spray for each. After putting it on their engine analyzer, shop came back MAF sensor defective. They replaced the sensor. Made a huge difference in idle and overall perf of engine.

The air mass sensor is a wearing part and will simply fail at some point. But its accurate measurement of the amount of air is incredibly important for the engine to run. That's why it's just as important that the intake system is airtight and the O2 sensors are working correct.

 

[taj1991]

2005 chevy tahoe Z71 (5.3 gas)
Need a little help here men. In May this year, I needed the head gaskets replaced. Unbeknownst to me, the repair shop installed 799 heads off a 2012 Suburban instead of the original 706 heads. Long story boring, since getting the truck back the CEL has popped every 2 weeks with P0171 and P0174 codes and I've been chasing the problem it seems. My question is, would those different heads be causing the PCM trouble to map the air flow thus throwing those codes? Also, should the PCM have been flashed/tuned for those heads or would the milling have been enough? Any thoughts are welcome.

 

[nonickatall]

If you have a lean mixture on both banks, I would first check all the related parts, regardless the cylinder heads.

And first I would check for air leaks, that is most likely, probably the intake assembly is not mounted correct, or they forgot a hose, for example from the PCV,

Additionally check the air mass sensor, very important check the fuel pressure and check the o2 sensors.

And you can measure the compression. If the compression is equal, the engine should have the same amount of air in the combustion chamber and should inject the correct quantity of fuel, so you should have a correct combustion.