[Elite130]

I have a 2016 Camaro SS with the A8. Recently the car idles horribly and there is a noticeable misfire after it sits for anything over a week. The longer it sits, the worse it idles and misfires. It will sometime stall out. If I let it idle for a bit and warm up, the misfire goes away and the idle smooths out. When I take it out to the street, under light acceleration it will hesitate initially and then get moving. With the RPMs up the car sounds great, but once we stop at a light, it idles bad again. If I drive the car around for 30+ minutes and drive with the engine revved up around 3k RPM, the car will idle and drive great after that. No issues.

The Camaro is bone stock. Fresh fuel. Just had the high-pressure fuel pump replaced, new Cats, new filters, new spark plugs, oil is 1 year old but has 3k miles on it.

Any thoughts on why the Camaro acts like this? Have any suggestions to fix it?

[ctrlz]

No codes or check engine light? Noticeable misfire and no CEL?
Without codes I would suspect a leaky injector. Do you smell gas?
This is a good situation to hook up a scan tool and see what your fuel trims are doing.
Also, why were the cats and high pressure pump replaced?

[Elite130]

Originally Posted by ctrlz

No codes or check engine light? Noticeable misfire and no CEL?
Without codes I would suspect a leaky injector. Do you smell gas?
This is a good situation to hook up a scan tool and see what your fuel trims are doing.
Also, why were the cats and high pressure pump replaced?

There have not been any CEL popping up. However I have not scanned it yet for codes. I do need to do that.

As for the cats and HPFP... December 2022 with 12,200 miles, we were having idling and driving issues. The dealership told us the cats were bad. They were replaced under warranty, as was the MAF sensor. Premature cat failure is a known issue with 2016's. Then a year later, December 2023 with 12,800 miles, the car started having severe misfire and eventually never started. Dealer stated it was the HPFP. HPFP was replaced.

We purchased this car in March 2021 with 8900 miles on it. One owner, all maintenance done at local Chevrolet dealership. This car has been nothing but issues.

[ctrlz]

Elite,
Sounds to me like your original problem was never correctly resolved.
Did you ever have a CEL?
I ask because it is highly unlikely a catalytic converter would "fail" without throwing a code and lighting the CEL. There are sensors in place with the sole purpose of monitoring converter performance.

While a scan tool may show some "pending" codes, perhaps point to misfires in a certain bank or cylinder, I think it would be more useful to see what sensors are doing and how the car is compensating. I do suspect a possible vacuum leak, and if it's big enough to cause stumbling issues or poor idle, that will likely show up in fuel trims. The car will be adding fuel to compensate for the "extra" air that is leaking in.

Hate to say it, but I think the dealership tried to throw parts blindly at the problem without fully investigating the cause.

[SomeGeoffGuy]

If it was misfiring, then the check engine light would be flashing. Must be something else. Sounds kind of like a vacuum leak, but it wouldn't just get better after 30 minutes. Running fine under throttle, then stalling at idle, is textbook vacuum leak, though.

Hmmm... is the exhaust rattling at all? Sometimes the exhaust can rattle on something and cause the knock sensors to activate and the timing to get pulled causing the hesitation you are seeing. A broken engine or trans mount can do the same thing. When it warms up, it might get enough room to not hit. Just thinking out loud.

-Geoff

[Elite130]

SomeGeoffGuy. - Thank you for the response. You got me thinking. The clip on the PCV connection on the driver's side valve cover is broken. The socket isn't broken, just the clip that holds it on. I'm wondering if that is an issue. I haven't seen any oil residue anywhere.

[SomeGeoffGuy]

Originally Posted by Elite130

SomeGeoffGuy. - Thank you for the response. You got me thinking. The clip on the PCV connection on the driver's side valve cover is broken. The socket isn't broken, just the clip that holds it on. I'm wondering if that is an issue. I haven't seen any oil residue anywhere.

If it is getting unmetered air, that could definitely cause it. You won't necessarily see a lot of oil out of it.

-Geoff

[ctrlz]

A little unmetered air getting in will show up as positive fuel trims. A LOT of unmetered air will most likely cause a CEL. You can have both if you have a cracked pipe somewhere and the leak gets smaller or bigger as the thing flexes.
With the symptoms you described, the dealer should've taken the car for a drive with diagnostics hooked up, and the results should be on your invoice. This is how they justify the bill to GM when they replace parts like converters and fuel pumps under warranty, which ain't cheap. Two converters and a HPFP is probably $2000 in parts. Dealers don't get to throw those at the car and hope for the best. Out of warranty is a different game. They can "do their best" and charge the customer, who rarely has enough knowledge to understand.