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Dan
Dan, ASE Certified Technician
Category: Chevy
Satisfied Customers: 2270
Experience:  20 Year Factory Trained Current GM Technician
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2001 Suburban: V8 2wd When starting..Runs rough..car runs fine

Customer Question

2001 Suburban, V8 2wd When starting up cold (outside temp around 40F), car runs rich, smelling at tailpipe. Runs rough during first 5 minutes. After that, car runs fine all day. Check Engine light on, misfire P300 code. After car is driven for a couple hours checked faults when car came home - P171, too lean bank 1, and P174 too lean bank 2. I have replaced maf sensor and coolant temp sensor, not sure where to go from here. I have looked online about tech bulletin 3232, having to do with misfires cold and possible po171, and po174.

What do you think would be the repair now, I'm thinking I might need to replace intake manifold gaskets. I've heard these can be a problem on this model.
Thanks,
Allan
Submitted: 7 years ago.
Category: Chevy
Expert:  Dan replied 7 years ago.
Hey Allan,
Is this a 5.3L engine?

Yes, The intake gaskets are a problem on these engines for them leaking especially when cold. To test you need a scan tool that can display fuel trim data and watch the short term trim #'s and spray carburetor spray around the intake gaskets and see if the trim #'s go into the negative.
also check the air duct from the mass air flow sensor to the throttle body. Make sure all is tight and no leaks.
Checking fuel pressure would be another test to do. IF fuel pressure is low, it can cause this problem also.
Dan and 6 other Chevy Specialists are ready to help you
Customer: replied 7 years ago.

Thanks. I understand what you are saying. My scan tool only has freeze frame, does not display live data. How else can I check this? By spraying around intake with carbuerator spray, and see if idle smooths out or changes? If fuel pressure is low, is that the pump or pressure regulator? (Yes it is a 5.3L)

 

Thanks again for the quick response, I'll try these things in the next couple days.

 

Allan

Expert:  Dan replied 7 years ago.
If the intake is leaking bad enough, it will change rpm by spraying carb cleaner on it. you can try itand see what happens.
If fuel pressure is low, fuel pump most common problem. Check fuel filter though, make sure its not clogged.

Let me know what these come out to be.
Customer: replied 7 years ago.

thank you so much

Allan

Customer: replied 7 years ago.
Dan,
Just wanted to let you know the car is repaired. I replaced the fuel filter, found partially clogged. Lifted foam pad out of way under intake and sprayed carb cleaner. Had a scan tool with live data and watched short term fuel trim. It changed immediately. Replaced intake gaskets following this test...2 hours later the car was repaired and started with a perfect idle when cold. During my travels in my business (car wash repair at dealerships), I found at a Chevy dealer after talking to forman,there is a TSB for this exact problem.

Thanks again,
Allan
Expert:  Dan replied 7 years ago.
Thanks for letting me know.
They have a couple of bulletins on these. One for the Flex fuel engine for the gaskets leaking and another one for the intake warping.
Glad you got it fixed and thanks for using Just Answer!