5.3L dies at idle after running at operating temperature in cold weather

[greg716]

Like said above, most likely a vacuum leak, check the pcv hose at the rear drivers side of the valve cover, it is common to crack and leak back there and is hard to see if you don't look for it.
It makes sense it's a leak since it gets worse when it's cold out, more air gets in when it's colder due to increase air density. There is a maximum range on the idle air control, if the leak is bad enough, the iac will continue to close more and more as the engine runs to keep the idle down, all the way until the point where the iac is fully closed, then it has no ability to prevent a stall on throttle transitions or increases in loads like from the heater or ac. The iac needs to be in a range to let enough air in when the throttle closes. If the valve is closed from a leak, it cant respond open fast enough to save a stall. Once you turn the truck off, then start it again, the iac resets, and the whole process starts over again.
When you first start the truck cold, what do the rpms go to right after fire up?

Depending on outside temp, anywhere from 800ish up to 1200ish. For example, this afternoon it was around -5F and the initial idle was around 1200-1300.

I haven't yet had a chance to chase down any vacuum leaks but I'll check the one you suggest.

 

[Jeremy79]

I am having a problem with my 2001 Yukon starting when it's colder then -12 will start at -11 and once it's running it runs great already done intake gaskets and exhaust manifold gaskets and cam sensor it has 50 psi when running I am the check valve in pump is bad could this be a problem when it's cold when it's -11 if I cycle the three time it will start and run looking ideas there are no engine codes thanks in advance

 

[Fless]

I am having a problem with my 2001 Yukon starting when it's colder then -12 will start at -11 and once it's running it runs great already done intake gaskets and exhaust manifold gaskets and cam sensor it has 50 psi when running I am the check valve in pump is bad could this be a problem when it's cold when it's -11 if I cycle the three time it will start and run looking ideas there are no engine codes thanks in advance

Use your fuel pressure gauge to document your key on, engine off (KOEO - engine not started) fuel pressures before starting. Measure it with one key turn, then a second, and a third, to see if it pumps up. Post the numbers you read.

If you've replaced either the cam or crank sensor, do a CASE relearn with a capable scanner. It might not help but do it to rule out any issues with that; it certainly won't hurt.