Q: My 2012 Chevrolet Silverado 1500 extended cab is my third Silverado; I've had two gas engines and one diesel. This truck is gas, the 5.3-liter engine with active cylinder management. I exclusively use good-quality Shell gas and no generic brands. I keep the truck in pristine condition, change the oil at the dealer every 3000 miles. I bought the truck with 3500 miles on it, and it currently has 9000 miles. Ever since I got it, I've noticed that, when stopped at a light in Drive, with the tach stable and showing 500-550 rpm on a warm engine, the idle tends to be just a bit rough. Sometimes it's fine, but mostly it's just rough enough for me to notice that it is not running smooth. I did not have this in my previous two Silverados.

I had the dealer check it out. The techs found that everything is running within spec, no miss, and no fault codes in the memory. They concluded the truck is running as it should, and there is nothing they could do to adjust this very light roughness in the idle. Is this true? Is there nothing they can do to smooth this idle issue out? Have you heard about this? The problem is not so big that it is a true major issue, but nevertheless I do notice it. Do I just need to live with it?

A: Rough idle can be a gray area, and sometimes the root of the problem isn't the engine itself, but the engine mounts supporting it. I don't see any applicable technical service bulletins on a rough idle or vibration complaint. The best thing to do is kindly request a test drive in the same model truck with the same engine/driveline/suspension configuration at the service department. If you drive the test truck and it feels the same, it's more than likely just a normal characteristic of the vehicle. If there's a significant difference that you can confirm with the service advisor or technician, further diagnosis is warranted. Keep in mind that you will typically get more of a vibration felt through the chassis with the A/C compressor engaged. This is a significant load on the engine, which is compensated in real time with engine speed being increased by a PCM command. When the A/C is turned on, the compressor still cycles on and off with refrigerant pressure. That could explain feeling it sometimes. So try it with the A/C turned off. That your older trucks seemed to idle smoother that the newer model doesn't confirm there's a problem. No two are exactly the same.


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