Intermittent CEL and Erratic Idle

SirManny · October 14, 2016

Maybe someone has already touched on this topic but i have never had a vehicle do what my 2016 Sierra CC SLT with the 5.3l and 8 speed trans is doing. I had a 2014 Sierra DC with the 5.3l and 6 speed trans and never had any of these issues before or after the headers and tune. So for the past few weeks my truck will throw a cel and it will stay on for a few days and while it is on the truck will have erratic idle. Sometimes the rpm bounces back and forth from 800 to 2500 as if someone is reving the motor. Then it goes away and the truck drives normal aside from the ridiculous/rough shifting and banging that the 8 speed does that the dealer and gm say is normal. The cel will go away for a few hrs or sometimes a day or two and come back and all those symptoms return. Today the truck acted like it wanted to stall on me and took a lil effort to get started. I called the GMC dealer and they said it would be two weeks before they could even touch the car. I called the Chevy dealer and they refused to do any warranty work even though they are the closer GM dealer to me of the two. They also said it would be a week before they would be able to get to it and neither dealera had loaners available. So I ended up calling GM customer service and they worked it out to where a different chevy dealer will tow my truck in on monday and give me a loaner. Has anyone else had a similar issue/situation and if so what was the fix. My truck only has 9k miles.

Brianibew · October 15, 2016

Make sure all your spark plug wires are firmly connected, lots of threads on here with similar problems that ended up being just that.

SirManny · October 15, 2016

Make sure all your spark plug wires are firmly connected, lots of threads on here with similar problems that ended up being just that.

I will check those in the morning. Thanks.

InertiaFaze · October 15, 2016

Hey SirManny,

Based on there being a Check Engine Light there will be a code, either Active or History that will be starting point to figure what is wrong. I suspect that was obvious. Haven't heard of those exact symptoms but best thing is to start with the code(s) and go from there.. Good Luck!

SirManny · October 16, 2016

So today after checking the spark plugs and wires the cel wouldnt go away so i went to autozone just to have the codes read. The codes were for bank 1 and bank 2 too lean. So i went home checked all hoses and connections for the catch can and clean side seperator and everything was snug and tight. So not really sure if i should take the entire catxh can out and reinstall the factory pcv line before going to the dealer or just leaving ir alone. I had a catch can on my 14 sierra, 11 camaro ss and 13 sierra with no issues. So any ideas?

Brianibew · October 17, 2016

Just a thought, are you running e85 in a non flex fuel truck? Running e85 without the the proper equipment will cause it to run lean since e85 requires more fuel to run the same.

SirManny · October 17, 2016

No my 2014 was e85 but not my 16. I run 89 mid grade in it. This problem just started about 2.5 weeks ago. The lift and catch can have been installed for a little over a month now.