Evap codes, Bad gas mileage & Rough idle

[plinko]

Okay, so a bit of a long story here...

We bought a 2009 Vibe at the end of July, about 73K miles on it. A week after purchase (after we foolishly declined a warranty, thinking that it would be fine since we were buying it from a dealership) the CEL came on. After having Autozone check a few things, we ended up being told that the alternator's diodes were bent and corroded, and it wasn't properly charging the battery. We had the alternator replaced, lights went away, everything seemed fine.

Less than a week following that, it hit the top of the temperature gauge thanks to a radiator leak, so we had that replaced.

And then the CEL came on. Again. And again. Each time it's given a slightly different code in the Evap system. We tried just replacing the back valve first but that didn't work, so the entire canister and valve got replaced. After the light came on again we had the front valve replaced as well, and now the light's on AGAIN, giving the two codes for a loose gas cap or a hose leak (both the large leak code and the small leak code, I can't remember the numbers at the moment). We tried a generic gas cap from Autozone and now an OEM gas cap that's the actual part for the Vibe and the light's still on after several engine cycles. Additionally, the gas mileage is TERRIBLE now (we got about 140 miles to 3/4 of a tank of gas, driving on city streets to and from school and work) and filling up the tank has become an issue. The last two fillups, the pump has clicked off repeatedly, even after only getting a gallon or two in. Also, it's occasionally idling rough. Not constantly, but once the car warms up, it shudders as we're coming to a stop and occasionally while waiting at lights. Never for more than a second or two, but it's a noticeable, hard shudder.

The only thing I know of in the evap system that hasn't been replaced is the hose going from the canister in back to the front of the car, and the gas tank itself aside from the cap. I doubt the vaseline on the seal trick would do anything since it's a brand new cap. Anyone have any ideas as to what might be going on? A different shop suggested that we might have a fuel control problem causing the bad gas mileage, but they also want $140 to test the evap system and I'm not keen on paying them just to tell me what's wrong (though that may be normal, I'm admittedly not sure about that). My usual mechanic is awesome with repairs, but I think he's not so great at diagnosing problems.

[circuitsmith]

Sounds like you spent close to $140 blindly changing parts.
EVAP problems can be challenging to diagnose; near impossible over the internet sight unseen.
You need to find a mechanic that can test with a smoke machine to find the leak.

[tpollauf]

First off ... Welcome to GenVibe. We need a LOT more info on this Vibe to start giving you suggestions. As I read your LONG post (thanks BTW) the first thing that came to my mind was "what abuse did this Vibe get handed to it in the past 6 years"? Why was it on the market in the first place? Did you buy it from a dealer OR a private seller? Do you have an accurate history of what was done to it by the previous owner(s)? What area of the country are you located in (update profile please). Did it have a clean title? Could this have been a "flooded" car (a lot of them are out there)? Engine size & trim level? So many other questions that need answered. The vast majority (I'd bet 99%) of all 2009 Vibes have had ZERO problems in their first 60k miles or so. These are very reliable & dependable cars so something definitely happened prior to you purchasing it. Give us a better history of how you acquired this Vibe and maybe we can help then. Thanks

[plinko]

Hey, thanks and sorry about the info I left off!

We're in Texas, and we did get the Vibe from a dealership. It's not a flood car that we know of - we checked Carfax prior to purchasing, since we're in Houston and flood cars are a pretty big issue in our area - though I'll admit that we also didn't have it inspected before we purchased. This is the first car we've ever purchased, and naively I thought that because it was from a dealership, it would be okay. My mistake, I'll definitely admit that.

It's a 2.4L 2WD automatic model, clean title, if that helps. I just got back from the mechanic last night and he's baffled - he's run through everything on the TSB to test the evap and emissions and there's no leak anywhere. The smoke never came out anywhere and he's mystified and frankly so am I. The upside is that he's a great mechanic and didn't charge for the test since he can't find anything wrong... but the light's still on and we're still getting lousy gas mileage and intermittent rough idle. The issue with actually filling up seems to be the station we were going to so at least that's off the list.

His next step is going to be to call a friend at the GM dealership Monday to see if they have any ideas. I'm wondering if this could potentially be the ECM/PCM acting up? I know there was a recall for the 03-08 models for that reason and clearly we're not under that. It's certainly not giving any error codes for the ECM, it's just giving two loose gas cap codes, but it's a brand new OEM gas cap and we're screwing it down tightly, and there's nothing wrong with the seal or gas neck either.

I know you guys can't diagnose things over the internet, I was mostly just wondering if anyone else had experienced or heard of issues like this - I love this car despite the issues and I figured I'd ask the dedicated Vibe fans here.

[ctgottapee]

His next step is going to be to call a friend at the GM dealership Monday to see if they have any ideas. I'm wondering if this could potentially be the ECM/PCM acting up? I know there was a recall for the 03-08 models for that reason and clearly we're not under that. It's certainly not giving any error codes for the ECM, it's just giving two loose gas cap codes, but it's a brand new OEM gas cap and we're screwing it down tightly, and there's nothing wrong with the seal or gas neck either.

The 09 model year is completely different than the 08 so the recall would not be related

[trb]

Welcome fellow Houstonian! Which dealer did you get it from? I usually look online at all of the local Vibes for sale, hoping to find a nice manual 09-10 with the 2.4L to test drive.

Great that you have a good mechanic working on it, but I know those evap problems are a pain. I too wonder about the history, as my 2010 GT was trouble free in 75K miles. If I still had it, I'd offer to look at it and we could compare the two systems/swap parts. My 03 has evap codes, but then it has 220K on it. At least you got the inspection and plates and they are good until July before it has to pass the emissions test, but you certainly want to fix it due to the other issues.

FWIW, I've had very good service at the Beck & Masten dealer on FM1960 if you need to have a dealer look at it. We take all of our GM vehicles there for service that I don't do myself.

Good luck!

[vibrologist]

I wonder if one of the sensors is faulty or disabled by dirt or a loose electrical connection.
Did you make sure that the rim of the tank filler is clean and smooth? Any roughness there can cause a leak.

Also look for other reasons for extreme fuel consumption and rough idle: plugs, clean TB and MAF sensor, vacuum leaks on the intake side etc.

[jasonvibe]

to do A PROPER evap CAN TEST. the one solenoid VALVE SHOULD BE BYPASSED ALLOWING all the smoke to enter the entire system. I also am having odd issues. But no codes. I will post on another topic