Hi, I need some help here. I have an 08 chevy silverado with the 5.3 liter motor. I am having problems with my truck idling rough. When starting the truck cold it idles rough, but once motor has been warmed up it idles fine. I have cleaned throttle body, replaced mass air flow sensor, and new spark plugs and wires. The fuel pressure is good as I have tested that as well and the pump is a year old(not that new ones cant be faulty). I also notice if i drive the truck while it's idling rough it doesn't like to take off act kind of sluggish and choppy, but if I let it warm up it drives fine. I dont have any trouble codes either.

 

Genuine plugs from a local parts store? ebay and amazon are full of counterfeit plugs.

Could be a vacuum leak. Check all hoses and the intake manifold for leaks. There's a hard hose that plugs into the back of the pipe on the left side that runs to the intake that I always forget to plug back in.

I'd check compression in all cylinders and I'd monitor it for misfires. The Torque pro app and any elm327 device should show misfires. My new favorite device is the Autel/Hyper Tough HT200 at Walmart. It'll read all the modules in the vehicle as well.

All the 5.3L's generally have a shake/shudder when idling. If you've never changed your engine and trans mounts, I'd change them. I recently went through this same thing with my suburban. Monitoring software showed no misfires but you could really feel the engine shaking the car. I had previously replaced the left engine mount and trans mounts but hadn't yet done the right engine mount because it's a pain to do. I managed to get the old one out and the new one in. It feels like it's brand new again. Absolutely no engine shake noticeable within the cabin anymore.

 

The truck has only 68,000 miles on it. I dont have an engine shake. It just idles really rough. To the point where it seems it's going to stall, but never actually does. The plugs and wires I put on the truck are from local parts store. I am going to see if I can find a vacuum leak.