Mostly stock 2006 gmc ccsb 5.3L
Doesnt want to idle in the morning with just hitting the key
Have to rev it a few times
Rough idle that sounds like it has a cam at times
Has po172 and po175 codes
Maf readings 4.3 g/s
Load at idle is reading 18%

I've swapped out maf and map for working ones with no change
Truck runs fine when driving down the road with no stumbles on take off
Tried spraying carb cleaner around vacuum fittings and intake with no change in idle

 

also checked fuel pressure @ idle 62 psi

 

Sounds like a vac leak..
How many miles?

 

99xxx

 

i always thought a vacuum leak would give you positive fuel trims????

 

I'd try swapping injectors and plugs from one side to the other and see if the trims follow. May have an injector that's fueling too much, or a plug that's not firing.

 

Both sides are reading -19.5 long term fuel trims. So i doubt its that. Matter of fact i just drove a 300 mile trip today and got 20.1mpg

 

Ive been thinking about this one and cant come up with anything good

The computer is injecting too much fuel and is on the verge of misfiring in the morning since it is in open loop. Once it warms up slightly and goes into closed loop it recognizes the problem and pulls injector spray time way back and throws the code...

Now the question is why is it injecting too much fuel to begin with...the fact that its on both sides make an injector unlikely, and the stated fuel pressure is fine...Your gas mileage is testament that the o2 sensors and injector trims are doing their job.

So to answer your question, I have no idea, but maybe my rambling will give someone else an idea.

Try checking the spark plugs.... insufficient plug gap may look like a rich condition due to incomplete combustion to the o2 sensor. Factory spec is around 0.040

 

Unplug the MAF and drive it and see what happens. The intake vacuum leak issue seemed to stop around 04 or 05. I don't know if thats when the teal green gaskets went into production or what but I just haven't seen that as a leak.

I've seen clogged cats cause negative fuel trims but that was bank specific with major drivability issues.

 

Id look at the o2s