2008 Aveo LS, Chugging/Rough Idle, No CEL

Hey y'all.

Just picked up a 2008 Aveo LS as a beater, and have begun some maintenance on it. I will explain the rough idle, but here is what's been going on so far:

- Initial CEL popped, showed codes for random misfire. I replaced the valve cover gasket, and all spark plugs.
- Idle remained rough, CEL cleared and no more misfire or oil on spark plug #1. Changed oil, filter, and oil pressure switch.
- On a quarter tank of gas, I dumped 3oz of seafoam into the crankcase, and 3oz of Lucas Oil injector cleaner/upper cylinder lubricant.

Car is running better, BUT I still have a rough idle. I do not hear a vacuum leak, but I cannot rule this out. Vehicle has 164k, is a 5M/T, have dealer receipts from previous owner. Dealership replaced fuel injectors, checked fuel pump (did not replace), replaced timing belt and components, as well as exhaust from the resonator back.

I do not know if timing was done properly, it's possible the tooth is off by 1. If anyone has had similar issues, I'd love to hear from you. In the meantime I'll be digging through the forums.

Please forgive me for any formatting ugliness, I'm on mobile.

Do you have any diagnostic tools? A multimeter is a must, and an OBD realtime datastream reader is extremely helpful. Also a vacuum gauge and compression tester are also a big plus as well. As a for instance, the compression tester would answer your question about the timing being off.

Thanks for the quick response.

I do have a multimeter, and a basic OBD scanner.

Do not have a vacuum gauge or compression tester.

I would be taking another look at that timing belt rotating the crankshaft completely through to make sure all the timing marks line up every rotation.
The reason I am saying this is because you are questioning it yourself because you installed the new belt. Always check your work. No rushing through anything.

You could check the timing marks as Ken suggested, however running a compression test would not only check that, but also the overall internal health of the engine as well. Perhaps you can rent or loan (AutoZone, etc) a compression tester. And, just an aside, that what you wrote made it clear to me that a shop had done the timing belt for the PO.

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Originally Posted by avguy

You could check the timing marks as Ken suggested, however running a compression test would not only check that, but also the overall internal health of the engine as well. Perhaps you can rent or loan (AutoZone, etc) a compression tester. And, just an aside, that what you wrote made it clear to me that a shop had done the timing belt for the PO.

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Yes, I agree on that compression test and getting that rental from autozone. It would be a lot faster then removing the covers for a physical check.

Thanks so much this far.

I checked harbor freight, I can get a compression test kit for $30 before coupon.

I have been looking at compression test guides, there seems to be two ways to do it: with the gas pedal all the way down (WOT), or not depressed at all. Which manner should I be doing the test on the Aveo?

Additionally, could it be a dirty IACV?

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Originally Posted by zaksglass

... I checked harbor freight, I can get a compression test kit for $30 before coupon. ...

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Absolutely a good thing to own one of your own. I'm not sure of the quality at that price, but it probably would be 'close enough'

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.... I have been looking at compression test guides, there seems to be two ways to do it: with the gas pedal all the way down (WOT), or not depressed at all. Which manner should I be doing the test on the Aveo?...

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Constant WOT. And first start it up, and then pull the fuel pump relay and let it stall out. Run the test dry first (no oil added). Then, if the compression is lower than 190, squirt a small bit of motor oil into the cylinders before cranking to see how much (if any) the compression comes up.

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... Additionally, could it be a dirty IACV?...

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Yes, along with around 200 other possibilities, which is why a systematic diagnostic approach is so important.

I would start with the most simple options. #1 what spark plugs were in it when you bought it and which ones did you replace them with? If they were anything but generic copper plugs, that may definitely be your problem.
#2, check to ensure there are no air leaks in the intake portion
#3, since you have an obd2 scanner, check the temps that the o2 sensors are sending (calculating because they aren't simply thermometers). Could have a clogged cat.
#4, fuel pumps can be goofy but did you also replace the fuel filter? If not I would definitely have a look at replacing that.
#5, go ahead and check compression and what not. Hopefully it's nothing bad.

Update/reply:

I did replace all four plugs when I got the car, they were Autolite crap and I replaced with fresh platinum NGK plugs. Compression came back, all four cylinders were very close (1-3psi). The fuel filter is a strainer within the fuel pump assembly, so I'd have to pull and replace the pump (not a big deal).

BUT I definitely have a failed head gasket. Some white residue appeared under the oil cap last week after a few miles of driving. Just yesterday all of my parts came in.

I will now be replacing:

Head gasket
Camshaft seals
Ignition coil
Spark plug wires
A couple of vacuum hoses (they're old)
Downstream O2 (just need to borrow a buddy's blowtorch)
Replacing the valve cover gasket since it's already been seated and driven

My OBD2 scanner is very basic and just displays codes. I think my local Harbor Freight has a detailed scanner on clearance, will look into further.

Will post an update when I have one.

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Originally Posted by zaksglass

... Compression came back, all four cylinders were very close (1-3psi). ....

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Even compression on all cylinders would be uncommon for a blown HG, unless the gasket was damaged evenly (which would be quite unusual). What were the compression readings? Did you remove the coolant overflow tank cap to see if there was any bubbling in the tank during the compression test? If not, do you have any other evidence of a bad gasket?

The 'white residue' could be something as simple as normal condensation which didn't have enough time to get burned off because the engine wasn't sufficiently hot long enough. It would be really disappointing to do the gasket, only to find out it wasn't blown at all, and not the cause of your performance issue.

There was some bubbling. I drove it a couple weeks ago after changing some ignition/intake parts, it ran smoother. Drove about 60 miles on the highway, and I burned coolant and oil.

The timing parts will be the first to come off. I had suspected the timing was off a tooth, but after burning coolant and oil figured it was the head gasket.

Edit: Forgot to mention that even though it ran smoother, I still had a rough idle and misfire, on top of burning coolant and oil.

For what it's worth, several people have reported that platinum plugs have caused problems with their Aveo and better luck with regular copper and/or Iridium plugs.

It might be worth getting some new cheap-ish copper plugs to test

Got down to the timing components today. The front camshaft sprocket is off by two teeth.

Cylinder head came off today.

Head gasket had utterly failed - almost no seal left, it was pretty much bare metal.

Replaced gasket and got the cylinder head back on. Currently plugging things back in and replacing some other parts. Having trouble with a few vacuum lines off the battery side of the intake manifold, I'm not sure where they go.

Go to gmpartsdirect.com and look up the car and search around in emissions I think. They have exploded views of most parts. Saved me multiple times.

Oh and I definitely know about not using the Platinum plugs. They just cause our engine to run like crap. The last time I tried it misfired like crazy and stopped immediately after changing back to copper plugs.

Good to know thanks so much for the reply.

I'll dig through GMPartsDirect. Will also order copper plugs.

So how did it go?

It's all back together right now. New head gasket, plugs, wires, ignition coil.

Car cranks hard but will not turn over. Fuel pump primes and runs when the key is turned, so I'm not sure what's going on. Will look at it later today.

OK SO IT FINALLY STARTED AND RAN TODAY!!!!

Ignition wires were mixed up. Simple as that.

Car started, ran rough, CEL came on and I stopped her. Two codes, P2076 and P0303. I had mixed up the vacuum lines on the EGR Canister, simple as that.

SO NOW I JUST HAVE P0303, CYLINDER #3 MISFIRE. I'm at my wit's end with this car.

water in oil cud possibly b from oil cooler.... aveo is notorious for getting oil in coolant.... so just be aware might not be head gasket...I wud invest in complete gasket set... cheaper than buying one at a time... Ebay has it for$50