Mechanics

ROUGH IDLE

2003 GMC Envoy

Engine Performance problem
2003 GMC Envoy V8 Four Wheel Drive Automatic 81000 miles

I keep getting a P0171 (system too lean) code. I changed the wires, plugs and fuel filter. It idles real rough in the morning. After it warms up and I drive 5-10 miles or so then everything runs fine. Could it be the O2 sensors? The MAF sensor is reading 3.49 on my scanner which I believe is normal.
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Kslusher1
October 29, 2008.




If you have to crank it quite a few times to start it cold, check the cold start injector. If this isn't working, it will run rough until it warms up.
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Tiny
James W.
Oct 29, 2008.
I checked the codes again and I had 4. 2 lean codes for bank 1 and 2 for bank 2. It cranks and starts fine. It just runs bad after it starts.

Tiny
Kslusher1
Oct 29, 2008.
Sounds to me like the engine temp sensor is telling the computer that the engine is warmer than it is on startup. Thus, giving the motor too lean a mixture until the actual motor temp catches up with the sensor reading and then everything is ok.

Tiny
James W.
Oct 30, 2008.
The engine coolant temp sensor?

Tiny
Kslusher1
Oct 30, 2008.
On my scanner it is showing the ECT and the IAT at about 20-30 degrees difference. Is the IAT sensor and the MAF sensor one unit on a 2003 envoy xl with a 5.3? Mitchell 1 online manual is only showing the 4.2.

Tiny
Kslusher1
Oct 31, 2008.

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