P0171 Driving me insane - Totally


New Member
Guys, need some help with this as I have run out of options. 04 Envoy with a 4.2 is what I have.
Since late summer the truck has been really hard to cold start, rough idle, hesitation, loss of power. Once she warms up idle is not too bad, a bit high at times. Sometimes takes 5-10 tries to get a cold start. Also, you kind of have to leave the gas pedal alone. As soon as you hit the gas the engine will stall out during cold starts.
So far these are the part I have changed.
New SAIP solenoid, new front O2 sensor, new spark plugs, new coils, new MAP sensor, new intake manifold gaskets. I also changed the valve cover gasket since I was already halfway there.
I also cleaned the throttle body as well as swapped out to another TB just as a test.
Tested the air injection pump as well. I have good suction as well as it's blowing hard thru the pipe.
Also checked out the fuse that powers the SAIP solenoid.
Any help would be appreciated, as this is my winter truck and really want to get her back on the road.


Well-Known Member
I've got the same code a few weeks back and the engine shut off while my wife was driving. She was in traffic at the time. She was able to get it running again after throwing it into park and starting it again.
This morning the truck would not start,tried switching the fuel pump relay and no dice I thought it maybe a battery issue so I got it jumped and still nada.

I'm picking up a fuel pump tomorrow morning since everything else seem to check out. Throttle body is clean and not sticking, maf sensor is clean and no air leaks. This is where I am at with my diagnosis.


New Member
I changed the fuel pump a couple of years back as the lines were all corroded on the old pump. I would be surprised if that were the culprit. To change it is a huge PITA.


Platinum Supporter
Try replacing the Camshaft Position Sensor, then doing a CASE Relearn. I swapped mine out after a long time of troubleshooting issues with high idle and lean problems. That solved everything.
So this past week I replaced the fuel filter. Made no difference in startup behavior.
Last night replaced the cam sensor and the valve timing solenoid. No luck, same issues.
I will order a new fuel pressure regulator, see if that makes a difference.

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