it's normal....no worries,it's the cam. here's an earlier thread on the subject

https://camaroforums.com/forum/showt...ght=rough+Idle

 

This afternoon, while getting onto a freeway, something broke free. Suddenly there was a really noticeable increase in power and simoultaneously the engine smoothed out. I think this happened once before but it wasn't quite so dramatic; made me wonder if it actually happened. This time there was no doubt.

The car ran smoothly and with more power for the rest of the drive home. Never-the-less, I've got an appointment with the dealer tomorrow morning and I'll take it in as I can still hear what sounds like a noisy lifter. It's especially noticeable in 3rd at 1.5K rpm under light load.

I'm thinking that with hydralic lifters, there should be almost no noise from the valve train; certainly no tapping or knocking.

 

Just for my peace of mind, I'm getting a second opinion. The place where I bought the car is the Northwest's Chevy high performance center. They specialize in Corvettes and Camaros. I'm taking it there Thursday. If their techs tell me she's good, then I'm good too. (I figure if people get a second medical opinion, why not a second mechanical opinion.)

 

Update on rough idle:

After the idle relearn procedure, the rough idle returned and I began to hear a knocking sound in the engine at between 1.5K and 2K rpm. It was intermittent and its frequency varied with engine speed. I took it back to the dealer and had a tech drive the car with me in the passenger seat. He couldn't duplicate the knocking and told me the rough idle was normal. I wasn't really convinced so I figured I'd have the dealer at least change the oil and filter just to be sure I wasn't driving around with oil and a filter that had been left in by the previous owner and not changed by the dealer from whom I bought the car.

About 2 days later, the knocking got significantly worse and there was a roughness in the engine at all RPMs. Back at the dealer, the same tech went out to the car and listened to the engine. This time he heard the knock and he felt the roughness.

That was Wednesday. Thursday morning the car went into the service department for troubleshooting. The car has thrown no codes and normal diagnostic and analysis have failed to reveal what is going on. After consulting with GM, the techs are tearing down the engine. So far they still don't know what's wrong with it and it's Friday afternoon.

I'm betting on the hydraulic lifters being shot.

 

The service department just called. Turns out they had to replace the hydraulic lifters. I pick it up tomorrow morning and will see if things have smoothed out.

 

I picked up the Camaro at the dealer yesterday. They replaced 8 hydraulic lifters. If I'm correct, the engine has 16 hydraulic lifters: 8 for the intake valves and 8 for the exhaust valves.

The invoice didn't specify which lifters were replaced and it being Saturday, there was only a service writer available and she didn't know and couldn't find out. In any event, the knock at 1.5K - 2.0K rpm is gone and the engine runs more smoothly than before though I haven't noticed any change in fuel economy. (Too soon to tell.)

This whole episode leaves me with a question maybe someone could answer as I haven't been able to find answers in multiple searches.

If the engine has 16 lifters, why did only 8 get replaced? I'm thinking that maybe the lifters for the exhaust valves are different from the intake valves so if one set shows signs of problems, it doesn't necessarily mean the other set is going to exhibit the same problems a short time/few miles later. Am I correct?

Thank you all for reading this and for any answers you may provide.

 

hey - glad to hear that the roughness is gone, but i too own a used ss and am noticing a similar symptom. When stopped at a red and idling i notice a bit of a 'shake' or 'shift' while in my seat. i was going on the assumption this was normal but after reading this, it may be the same thing you too felt.

Also notice a slight almost 'ticking' of the motor at idle. it's very minor at this point.

 

got same issue with my 2011 convertible 6 , not that pronounced though