2006 Silverado Rough Idle/Hesitation Mystery

[BigMroz]

Recently my 2006 Silverado 5.3 litre has been having some rough idle issues. The issues are intermittent, but most of the time the truck doesn't start idling rough until it is to operating temperature. Also, my truck has a slight hesitation from take off, never throwing a check engine light though. Recently I changed all the plugs with Ac Delco iridiums and put new wires on the truck as well. The MAF sensor has been cleaned along with the throttle body (the throttle body was barely dirty). After going through what I thought would fix the problem, I thought I would try some Techron in it, so I ran the tank down to about empty and threw some in and filled it up. The truck ran absolutely amazing with the Techron in the tank, smoothed right out, the rough idle and hesitation were gone. After I went through the tank filled with Techron and filled up with another tank of gas, the rough idle and hesitation came back... Does anyone have any ideas what could cause this, or has anyone had this happen to them? And by the way, the truck only has 66,000 miles on it...

[Formulabruce]

Fuel separation. There are some conditioners to stop it, but not much besides Toluene to "fix" bad gas.

Have seen fuel separate in less than 2 months in summer.

[Z45]

Throttle plate carbon.

 

[Dnt]

I have gazed into my crystal ball and like elcamino I have THE answer. You have not driven your 5.3 hard enough to keep the carbon blown out of it and the catalytic converter is partially stopped up. Have all three swapped out for new and BAM good as new. You can try a Italian tuneup but it is probably too late now.