Rough Idle from Failing EVAP sensor?
 

2012 SS LS3, had to have my EVAP sensor replaced recently when I noticed the check engine light come on. The dealership took care of everything and I was on my way. I has been about a month now and I'm noticing some rough idle. Not the cool kind from all of that HP :)

No matter if she is cold or hot, when sitting idle it will consistently come in waves about every 5 seconds. 5 seconds of smooth idle, then about 2 seconds or rough flutter. Its the same feeling as though the car is about to stall out, but not quite THAT bad. This is not noticeable through the RPM ranges, only idle.

The only performance mods I have are a K&N CAI and the VMAX CNC Ported Throttle Body - both of which have run fine before without rough idle. Any ideas on what is going on? I will eventually take it to the dealership when I have some free time soon, but I would like to know if maybe one of my mods is causing the issue.

Thanks guys!

**UPDATE**

Just got back from the dealership, and just as I had thought, they said "No Error Codes were shown" and that the mechanic said "I have an aftermarket Air Filter", basically insinuating that it is the fault of the CAI. I have to respectfully disagree. I've had that CAI on two of my Camaros and totaled over 20k miles of use on it without these symptoms.

I can't fault them though. By all terms and conditions, they are technically right. I DO have aftermarket parts on my car that could POSSIBLY be the culprit. I suppose it is one of those risks we all accept when we mod. I guess I'll take it to a third party mechanic for a second opinion, but short term, this is frustrating. Assuming they are correct and it is either/a combination of my CAI and Ported TB, what are some reasons my car would act like this? O2 mixture is off? I can't think of many other things. RPMs bounce between 500 and 300 when idle. With the recently replaced EVAP sensor, I'm more inclined to believe someone has bumped a hose.

P.S. Just as a FML for today, I had to take her in for

- Oil Change
- Leaky Radiator
- Loose Hand Brake
- Rough Idle

I open my garage in the morning to begin my day only to hear *TsssssssssssssS*. 14 PSI back tire. Picked up an industrial screw on my 4 day old tire. Whatever, I'll have them patch it at the dealership. I pick up my car and the attendant tells me "Yeeeeah, we have a new tire patching machine that poked a hole in your sidewall and blew the tire. Obviously they replaced it to the tune of $300 something dollars, but it just adds to the "pleasant" day.

Did the CEL come back on? Usually when a evap purge solenoid sticks open, it will cause a rough idle, and extended cranking when starting. Vapors from the gas tank collect in the intake and choke it out.

No, no check engine light coming on. Is it possible that with the CAI and TB the air to fuel mixture is off causing the timing to be off?

Sorry to see you're having some troubles with a rough idle after having some work done for it at the dealership last month. Let us know if you want to have this looked at again by them - we're available to provide any additional support we can.

Sarah (Assisting William)
Chevrolet Customer Care

So, I have not been to the dealership yet, but I did notice a couple things recently. The rough idle actually is notable throughout the RPM ranges. When idle at a light, I can hold it at about 2k RPM and I can still feel the flutter. I'm also noticing a big loss in horsepower. Normally I can "punch it" and feel it hit the torque band, but now it does not have the same power and there is even a moment where it feels like all power is lost.

Not sure if it could be related, but there is a little bit of leakage from my radiator cap. It does not look fresh, but when I look under the cap, the fluids admittedly look a little low. Sometimes when idle, my car will reach 220+'F. This cannot be normal, right?

I'll try to get some answers soon, but the issue is getting progressively worse :(

I would guess the monkey at the dealership was careless and either knocked a spark plug wire or yanked on some other wire or didn't make sure the connections were correct-locked when he changed the EVAP.

I hate to say it but,good dealership mechanics are few and far between these days.Seen way to many issues locally lately.

Think about...you say it happened rite after you got the warrantee work done

I can't say it was IMMEDIATELY, but it is the only thing to change in recent history. If it was something like a loose spark plug, wouldn't the issue stay consistent? Mine seems to be progressively getting worse. I'm thinking it has to be something with the timing or air fuel mixture. but I have been wrong before :)

Runawayhacker,

Apologies to hear about your vehicle concerns as I'm aware of the displeasure caused here. When you are ready, please let me know if I can be of assistance by monitoring the dealer's diagnosis on your behalf. If interested, you may also send me your VIN privately and I will research any recalls associated with your particular vehicle.

Kind regards,

William R.
Chevrolet Customer Care

Keep us posted. Will be interesting to know the resolution. Take it to a different dealer or let the Chev Customer Svc escalate for you.

BTW I get 220 deg at idle if not using the AC (even in the winter). With AC on it usually is < 200.

Shameless bump post to inform others of update :)

if it was a spark plug or wire you would have a light,did you have a diagnostic done or did they just do a visual insp to verify the repair they had done? Some dealerships wont diag anything without a light on especially under warranty,

There were no warning lights, but the dealer acknowledged the roug idle. The phrasing was "there were no error codes thrown up" (sorry, we're in the south ;) ). Honestly, don't even know if a scan was done or not because I brought my car in on a Friday with a laundry list of things to do. Perhaps they took the easy way out because they were tired at the end sof the day and though "well, if I don't have to troubleshoot it, I won't".

I was surfing around and found this thread. Looks like this guy at least had the same symptoms as me. I'm off to buy a torque wrench real quick so I can make sure the spark plugs are all properly secured. I'll keep you guys posted. Hoping that this is going to be the issue and is an easy fix.

http://www.camaro5.com/forums/showthread.php?t=121428

Just checked my MAF as well and noticed a few drops of oil on it. Bought some cleaner and made sure it was spotless. Made sure spark plugs were snug. Problem is still here .... :(

I DID notice a little "Omph!" from cleaning the MAF, so at least that was good.