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I have a 2000 GMC Sierra 1500. In the winter when I start it it starts fine but idles down to almost nothing and revs back up. It does this until it starts to warm up. I have been dealing with this since Nov 2010. I take it to the shop every winter and no one can find it. They say there is no intake leaking, have replaced and cleaned several sensors. Now they are saying fuel pump. I am at a loss. HELP!


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contributions: 1961
Images: 37
Location: Oregon
the first thing to do is leave your truck at a shop that can park it outside overnight and start it up in the morning with a scanner hooked up and see what the engine is doing (or what the computer sees the engine to be doing). Are all the temp sensor agreeing about the temperatures. what are the fuel trims showing? Check what the Idle Air Control is doing. Watch the Throttle Position sensor is reading. Look to see if you have any readings that are erratic (or more erratic than normal)

Have the fuel pressure measured if they think it's the fuel pump. fuel pressure for the 4.3, 5.0 and 5.7 are 60-66psi. for the 4.8, 5.3, 6.0 and 7.4 is 55-62psi.

usually an air leak, (vacuum leak) will cause the idle to go higher not lower.

some trucks have a problem with water getting into the computer's connector and causing problems.


   
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I have always left it overnight so they can see what it does. The place I left it Monday night said fuel pressure dropped below where it should be (can't remember what he said the pressure was but is dropped a lot). That is why he thinks it is the fuel pump or possible the fuel pressure regulator. I told him to change that first and see what it does after. I have not heard from him yet today. Last winter is the first time Service Engine Soon light ever came on and the codes were 171 and 507. As I said before this started in Nov 2010, nothing changed after mechanic replace MAF and one other sensor (can't remember which one). Next Nov (2011) they changed the fuel filter when I had it serviced and it went all winter with no problems. Late 2012 would do it once in awhile and in 2013 was worse. Has started off this winter bad. It has 127,000 miles on it has been overall a good pickup. UPDATE Just heard from the mechanic and he did find a leak in the intake gasket. Hopefully this will fix it.


   
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contributions: 1961
Images: 37
Location: Oregon
I hope they have found and fixed your problem.

when temperatures get cold it really does strain the things that make the engine work. The timing may seem coincidental but the problems that you had repaired are not the same things. It's not a repeating repair although it may seem to be a repeating symptom.


   
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