Sierra Hesitation on cold mornings
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Teching In
Joined: Dec 2015
Posts: 3
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Sierra Hesitation on cold mornings Recently bought a regular cab short bed gmc sierra with 4.8 for cheap. On first cold start of the day it hesitates when taking off and has a rough idle. I read codes...
P0101
P0174
P0171
p0442
p0449
I have replaced air filter, cleaned mass air, and cleaned throttle body, all of which needed done. Reset codes and didn't solve any of them. Wondering what the next step is with out just throwing parts at the truck. Once it is warmed up the truck runs great.
P0101
P0174
P0171
p0442
p0449
I have replaced air filter, cleaned mass air, and cleaned throttle body, all of which needed done. Reset codes and didn't solve any of them. Wondering what the next step is with out just throwing parts at the truck. Once it is warmed up the truck runs great.
2 of those codes are for a leak in the EVAP emissions control system, 2 are "system too lean codes", and one is a MAF frequency low code.
So I'd put my money on you have a vacuum leak with the EVAP hoses or the unit itself.
I don't recall if it's on the fuel rail or near the tank. But I would inspect it, the hoses are likely cracked and leaking unmetered air into the engine causing it to run lean until the system goes to closed loop and the O2 sensors start dumping in fuel to compensate.
So I'd put my money on you have a vacuum leak with the EVAP hoses or the unit itself.
I don't recall if it's on the fuel rail or near the tank. But I would inspect it, the hoses are likely cracked and leaking unmetered air into the engine causing it to run lean until the system goes to closed loop and the O2 sensors start dumping in fuel to compensate.
