2008 Aveo LS, Chugging/Rough Idle, No CEL

[zaksglass]

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.

[avguy]

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.

[zaksglass]

Thanks for the quick response.

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

Do not have a vacuum gauge or compression tester.

[Ken Jaworski]

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.

[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.

[Ken Jaworski]

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.

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.

[zaksglass]

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?

[avguy]

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

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'

.... 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?...

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.

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

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

[hexskrew]

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.

[zaksglass]

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.