Misfire / Rough Idle

2004 Aveo

Code P0300 - random misfire.
Changed Spark plugs and wires, ran seafoam (cleaner) through. Problem was fixed for about a month, started happening again.

Since i have changed the Coil, Oxygen sensors, and the fuel filter/pump. I've had a compression test and the compression is apparently good.

None of these have fixed the problem. I dont hear or feel the misfire, but the CEL flashes after about a minute of resetting the code. The engine idles very rough.

Anybody have any more suggestions? I'm considering swapping the ECU but am not sure where it is. Also considered swapping the Throttle position sensor. Is the TPS just part of the throttle body?

I basically just need to get the CEL off so I can sell the thing... but Im not a fan of just disconnecting the light!

Thanks a lot!

do the idle relearn, see if that helps. (i'm not sure 2004 needs it done).

mist your wires and coil pack with water while running and look for a light show. Also verify you put the wires on the plugs all the way and did you gap the plugs?

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Originally Posted by petrified.rabbit

(i'm not sure 2004 needs it done).

mist your wires and coil pack with water while running and look for a light show. Also verify you put the wires on the plugs all the way and did you gap the plugs?

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To make it easier to see any shorts in the spark plug/coil wires, shut the lights off in the garage, or wait until night time and do in the dark. I did this with a sunfire once and you could easily see which wires were toast.

Misted the wires, no light show. Pulled the plugs, it looks like only 2 have been firing. They are all pretty charred. Changing the plugs seemed to make a bit of a difference, but still not fixed.

Possibly bad valve seals?

<bump> having a similar issue (havent tried the light show yet though)

Definitely do what Rabbit said above, that is your best bet.

what does "mist your wires and coil pack with water while running and look for a light show" mean? I am in the fire service so I am much better at disassembling cars then I am with engine work, although I do know my way around an engine bay

take a spray bottle like an old 409 cleaner bottle, that was empty. Fill it with water, set it to spray not stream. Take the cover off your engine so you can see the wires and coil pack. Start the car, let it run a minute or two. Then using the spray bottle "soak" the plug wires and coil pack. If there is a short (causing a spark plug to miss) then the water will ease the resistance and the sparks will fly, creating a light show. Even if there isn't a visible light show if the water being sprayed makes the car chug, stall or ___ the part you are spraying most likely needs replaced. Doing this at night or in the dark makes it very easy to see the sparks. Do not touch the wires or coil park while its running, 40000 volts (or whatever our specific voltage is) kind of hurts, a lot.

wish i read that that before i pulled that plug wire while it was running,lol.i was 21 (1981)was trying to figure out which cylinder was not firing,so reached in pulled first plug wire and WHAAAMMM didnt relize dc current had that much power.no ill effects that i know of but wouldnt try again with out some good thick leather gloves on. ;)

My 2007 Aveo was running ok but thought it needed maintainence. Changed the oil and the plugs now runs rough. The Actron tells me #4 is misfiring, checked everything a dozen times all seems ok. Does the system reset after the battery has been disconnected.

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Originally Posted by petrified.rabbit

do the idle relearn, see if that helps. (i'm not sure 2004 needs it done).

mist your wires and coil pack with water while running and look for a light show. Also verify you put the wires on the plugs all the way and did you gap the plugs?

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What is the idle relearn? Having same problems

I don't mean to beat you up, but I want to understand what is going on... :)

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I dont hear or feel the misfire, but the CEL flashes after about a minute of resetting the code. The engine idles very rough.

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Misfire = "runs rough." Light flashing = catalyst damaging misfire.

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Since i have changed the Coil, Oxygen sensors, and the fuel filter/pump.

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That seems like a lot of money... change the oil too if it smells like gas.

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I've had a compression test and the compression is apparently good.

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Why do you say "apparently?"

If it were mine, I would be doing a power balance test to isolate which cyl(s) is(are) not contributing. I would check enhanced data for fuel trims and the misfire counters.
I might even inspect the timing belt, roll the engine to TDC and see if the marks line up, then do a cylinder leakage test if I am confident it is a mechanical issue.

If you disconnect that light, another might come on in it's place.

I think it makes more sense to either study and tool up or invest in a trustworthy mechanic. Misfire codes are complex and can be time consuming even if approached systematically. HTHY

I'm actually having a similar problem with my 2005. I haven't gotten a chance to check the plugs, wires, or coil packs yet. What happened to mine has happened gradually, it used to just seem to kind of buck out on the highway if I didn't have the RPMs up high enough and downshifting would seem to clear it up. Now recently it has become a real issue to the point that it has no power out on the highway whatsoever, even the slightest grade bogs it down. It is definitely idling rough, sometimes almost to the point is seems it wants to cut out. The check engine light flashes at first, then will stay solid on for a period of time then will begin flashing again. It's got around 75k and actually recently had the head rebuilt and the timing belt and idler pulley replaced so I doubt it is a compression issue. My biggest concern is that when I got in after work this evening I turned the lights on and the dash was completely dark which kind of makes me concerned there may be a more serious electrical fault at play here as I have observed the dash lights and clock brighten and darken as if maybe there was some sort of power regulation issue (??) Im certainly noe expert so any advice would be appreciated

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Originally Posted by DPjcarsnotok

I'm actually having a similar problem with my 2005. I haven't gotten a chance to check the plugs, wires, or coil packs yet. What happened to mine has happened gradually, it used to just seem to kind of buck out on the highway if I didn't have the RPMs up high enough and downshifting would seem to clear it up. Now recently it has become a real issue to the point that it has no power out on the highway whatsoever, even the slightest grade bogs it down. It is definitely idling rough, sometimes almost to the point is seems it wants to cut out. The check engine light flashes at first, then will stay solid on for a period of time then will begin flashing again. It's got around 75k and actually recently had the head rebuilt and the timing belt and idler pulley replaced so I doubt it is a compression issue. My biggest concern is that when I got in after work this evening I turned the lights on and the dash was completely dark which kind of makes me concerned there may be a more serious electrical fault at play here as I have observed the dash lights and clock brighten and darken as if maybe there was some sort of power regulation issue (??) Im certainly noe expert so any advice would be appreciated

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Sounds like a bad ground to me. Clean your contacts, and check the battery negative to body cable to see if it is corroded

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Originally Posted by DPjcarsnotok

I'm actually having a similar problem with my 2005. I haven't gotten a chance to check the plugs, wires, or coil packs yet. What happened to mine has happened gradually, it used to just seem to kind of buck out on the highway if I didn't have the RPMs up high enough and downshifting would seem to clear it up. Now recently it has become a real issue to the point that it has no power out on the highway whatsoever, even the slightest grade bogs it down. It is definitely idling rough, sometimes almost to the point is seems it wants to cut out. The check engine light flashes at first, then will stay solid on for a period of time then will begin flashing again. It's got around 75k and actually recently had the head rebuilt and the timing belt and idler pulley replaced so I doubt it is a compression issue. My biggest concern is that when I got in after work this evening I turned the lights on and the dash was completely dark which kind of makes me concerned there may be a more serious electrical fault at play here as I have observed the dash lights and clock brighten and darken as if maybe there was some sort of power regulation issue (??) Im certainly noe expert so any advice would be appreciated

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Sounds like a bad ground to me. Clean your contacts, and check the battery negative to body cable to see if it is corroded

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Originally Posted by Pickles

Sounds like a bad ground to me. Clean your contacts, and check the battery negative to body cable to see if it is corroded

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I checked the battery terminals they are totally clean, I followed the ground cable as far as the starter and it seems to be solid. I don't have time to trace it back to the body as I've got to head out to work momentarily, but it's still wrapped in the factory protective covering (that corrugated tubing wrap they put on it) so if there were a break inside there I can't tell, but that seems unlikely as it seems undamaged and fully intact. I also sprayed down the coil pack to check for the "light show" but saw no apparent sparks. Oh well, I guess I'll be pulling the plugs this afternoon when I get a chance. Thanks

Thanks for the advice regarding the misfiring issue, when I went to pull the plugs there was actually one snapped which of course caused my miss but nothing a new set of NGK iridium plugs couldn't fix. Apparently when the head was replaced the ^%#ing mechanic put the old plugs back in. Oh well, one less mechanic out there that will get my business. Huge relief though, running great now. However the dashboard cluster lights are still out as well as the passenger side front and rear running lights. I checked both fuse panels and the corresponding fuses are intact. In the engine compartment fuse panel there is a long white bar at the extreme right side of the box assuming you were standing looking under the hood. It seems to be some sort of module, don't know for sure what it is, but it is a rectangular white bar that looks as if it snaps into the edge of the panel box with a rectangular indentation that runs along the top side and a cluster of several multicolored wires coming into it from the bottom. The extreme edge of this bar looks as if it has become very hot and brown (smoked) at the top closest to the coolant reservoir at the right edge of the bar. I don't know if this is significant, but any advice would be appreciated.

If the dash lights, park lights, tail lights, and license plate lights are all out then the circuit isnt getting power. It would be a relay/fuses, or a line to/from the fuse box itself. I would start with the relay since you checked the fuses

That long thingy is a splice pack. There is one in my 08 sv hb underhood fuse box for several power feeds. also, one behind the IP way up and taped on the body harness for several ground feeds. I took pix on how to access the latter if ne1 is interested.

HTHY.

Sorry, was out of town again this weekend. The Splice Pack comes apart (unless melted itself together) similar to a connector. Think of it as a terminating connector that joins all the wire terminals together. Splice packs can experience fretting and poor pin tension/contact just like any other harness connector. take one apart if you're bold and curious and you'll see.

On a lighter note, saw 4 Aveos on the way home tonight. A new Record!

Could you please post the relearn procedure. Just replaced timing belt which included a new head. Now the battery light is on and the car keeps dying. I put the charger on it, then it starts up, runs great but dies when I take the charger off. Thank you.

that sounds like you didn't attach the engine ground wire.

[QUOTE=petrified.rabbit;185911]that sounds like you didn't attach the engine ground wire.[/QUOTE

That's attached if you're referring to the ground that attaches to the alternator bracket stud with a nut. That's the only ground I took off I believe.

I just checked. What I thought was a ground appears that it wasn't. However I don't remember taking a ground strap off in this process. Where would it be.

The dash and running light problem is in the junction box between the battery and radiator expansion tank. Remove the plastic cover and you will see at the end there likely will be burn marks. This is the subject of a potential recall from Chevy. An interim solution is to by pass the block and wire around the terminals.

As for the idle problem, I have been suffering the same issue and after a time belt change, both cam and crank sensors and plugs wires, the code 0300 is still there with rough idle and misfires. I am an old hand at timing belts as I have two of these cars since new. An 05 with 300,000 miles and an 06 with 200,000 miles. The reliability of these cars is decent and having done these procedures many times before, this is the first time I have encountered such a problem.

I have swapped the coils, the wires and the plugs to no avail. I suspect that this is a crankshaft relearn procedure problem since I replaced both crank and cam sensors at the same time. I will replace the old ones if no one responds.

Also, when the four plugs came out and showed soot on 1,2, and 4. Number 3 was clean, but wet with unburned gasoline. This is why I presumed a spark issue and swapped out the ignition system from plugs to coil but with no change.

Nice to have two cars the same that share parts!

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Originally Posted by BrassBallsInc

... I will replace the old ones if no one responds.

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You stole my response.

Well, it ran the same with both sensors replaced. So that's not it either. The last thing I can think of is the computer is retarding the spark timing somehow. As it runs it continually requires more and more throttle to stay on. The computer is always retarding spark for some reason.

Haven't read the rest of the thread yet. My initial response to this would be to do a relative compression test watching starter current over time using an oscilloscope (200ms time base, depending on how badly the equipment aliases.) if one peak is a little low, then I'd follow up with cranking compression, running compression, and leakage test (pressurize the suspect cylinder at TDC and see where it goes.)

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Apparently, I've replied to this thread before.
BBI: Anytime those components are replaced, you want to get your tech-2 or clone going and run the crank variation relearn. here's the kicker: the engine has to be at operating temperature, or it won't run. It's the best way to make false misfires go away. Not a good idea if you have a mechanically dead cylinder or one that has been washed with fuel to the point the rings don't seal.

I would try and dry out that hole and screw in a fresh plug (I just run the NGK V-power plugs, the waste spark ignition is pretty hard on anything you put in there. I might add a few drops of oil to help the rings seal (if the cyl walls are badly scored, they won't seal anyway.) It sounds like you've gone thru the ignition system already. Did your coil swap net any result?

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not all of our cars have splice packs in the fuse boxes
http://www.aveoforum.com/forum/f108/...tml#post192629
I'm still looking for the splice pack on this particular one

The idle relearn procedure is here somewhere if you're willing to search. Otherwise; IIRC our cars relearn every 4 starts anyway.

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sometimes an injector dribbles instead of spraying a fine mist, and sometimes it is on (or even just leaking out of the nozzle) all the time. Anyway, I hope the best for everyone reading this thread.

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but wait... there's more!

It seems like I owe this thread some splice pack pictures... those were part of the few that are corrupt in my memory card. I'll have to take some more some time soon!

I just replace the cables and Spark Plug, driving on the freeway I got Misfire / Rough Idle.

So my choices to try would be the crank variation relearn or the coil pack. Check engine and hold lights are flashing.

Ive had the same problem on my 2007 aveo and the car had ngk copper plugs in it and these engines dont run well on copper plugs so i put in ac delco platinum plugs part number 41-801and now it runs absolutely perfect i also think autolite double platinums would have worked as well part number app3923...problem fixed

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Originally Posted by Toyobrob31

Ive had the same problem on my 2007 aveo and the car had ngk copper plugs in it and these engines dont run well on copper plugs so i put in ac delco platinum plugs part number 41-801and now it runs absolutely perfect i also think autolite double platinums would have worked as well part number app3923...problem fixed

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You're entitled to express your opinion, but the experience of many here (including me) is that copper plugs run just fine. Can't tell you what the problem with yours was (or still is), but IMO it was not the fact that the previous plugs were copper.