I have a 2015 Silverado 1500 with 140,000 miles on it. Driving in city traffic bumper to bumper the idle sits at 500rpm and then goes a tad lower and the truck starts shaking or rumbling , go to neutral and raising the rpm and it stops. Took it to a garage and scoped it but general items no specific problem. Bought it used so did a tune up. Test ride out and back one hour drive. Coming back into bumper to bumper traffic it started the low rpm 500 and then bucked far more then prior to tune up. Got it to the garage which did the tune up put on the test for codes and showed only the odd cylinders mis firing and 2 fuel codes B1 on catalytic converter I believe. Mechanic seemed baffled but then maybe I should have paid more and taken it to a Chevy dealer who deals with them everyday. My buddy says check the cam????? Any input on what is going on? After running test and about 15 minutes later the idle was smoother and no vibration. The truck was not stop and go in traffic and as hot but it went away but second time this happened in traffic and it was worse after the tune up. Is this a catalytic converter problem or should we be looking elsewhere? Air on or off does not matter still bucks.
Any help greatly appreciated.

Thanks
Sterk03

 

You won't get better service at a dealership, but you do need a better mechanic. A rough idling engine should not baffle a mechanic. This guy was probably a useless idiot, or he didn't want to work on it.

What are the codes please?

He's probably referring the AFM problems these trucks have. Check your plugs to see if they're fouled.



It's very possible. This can be determined with an exhaust backpressure test.


Other than that, make sure you've covered the basics. Air filter, spark plugs, intake cleaning, etc.
Diagnostic data will be critical to hunt this problem down. (fuel pressure, fuel trims, MAF readings, etc.)

 

Thanks for all the input I will review all of it and get with them to see what they found. It just went through a tune up and replaced all items listed. pressure test sounds like a good idea it was mentioned about the catalytic being blocked but then it will idle fine for a while then goes back to rough with 1,3,5,7 cylinders running rough.

Thanks again for all info and just read the Tahoe post with similar items???

Sterk03