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Old 04-12-2012, 10:08 PM   #1 (permalink)
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aveo misfire idle new engine

I have a 2004 aveo, had the engine and valves redone recently. The shop reused the valve cover gasket and caused oil to leak into the spark plug wells. That caused a misfire, but after a new gasket and plugs, I still get a rough idle and misfire code. Only idles rough, under rpm, runs great. Also has a very small knock at 2,000 rpm....SOMETIMES. I'M SICK AND TIRED of these idiots telling other people with the same problem what its NOT. well duh, I know its not the left rear wheel bearing! It's not the maf sensor.....I know this because they don't use one! Spark plugs DON'T leak oil, mainly because they don't hold back oil! These people need to shut up and go back to world of warcraft and stop giving advice.
If any REAL technician has advice, please help. I am a certified motorcycle technician and have COMMON SENSE, unlike many other forum posters.
Ok the problem is random misfire, very rough idle, about a top fuel dragster. I have fixed the valve cover gasket and all plugs with ngk, so no more jumping spark. Still get misfire code, and still rough idle. I know coils RARELY fail and I don't have any vacuum leaks, and compression is good on all cylinders. I almost think the timing is off (maybe a tooth), but checked that when the cover was off...timing is on, close enough to not idle poorly. You techs know what I mean. I say techs because we are TECHNICAL not just mechanics. Anyone can pull a motor, but a tech can pull one AND put one together...without you knowing he was ever in there (maybe better than the factory did). I know some of the posters are just trying to help, ok, but please leave it to the professionals to give advice (at will). These forums are all flooded with dead end responses. Sorry to complain so much, now my fingers hurt from typing on this phone, and I have a headache.
And yes, I know what the p0300 code is, so you don't have to cut and paste it on my page....thanks.

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Old 04-13-2012, 12:51 PM   #2 (permalink)
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CKP relearn

there is a function called
CKP relearn for GM products , many non factory scan tools can perform the operation - Auto Enginuity can do it

2004 and later aveo engines do not interchange , if a later engine is mixed , with an early system , they will set P0300 DTC ,there is another thread in this forum about that .... i do not know what the resolution was .

have you measured vacuum at idle , Teed into MAP sensor line or Brake vacuum booster line .... intake vacuum should be right about 20" but more important the needle must not have any flutter or wiggle to it .

a dollar bill held over the tail pipe at idle will show if misfire is real or a ghost in the ECM , if the pulses always push the dollar away , there is no misfire , if any pulses are vacuum pulses attempting to pull the dollar into the pipe ..
there really is a misfire ...
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Old 04-21-2012, 05:40 AM   #3 (permalink)
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taking my stab at it, are there any grounds missing? are the ignition coils connected in the right sequence? baring that maybe the pcm is damaged, or a connection is lose
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Old 04-21-2012, 11:37 AM   #4 (permalink)
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is it random misfire, or is it pointing to a specific cylinder?

You did not say in your post that I saw. If a specific cylinder, do a compression test to eliminate valves not closing, then the obvious - coil, wire, injector.

If it is RANDOM misfire, then almost for sure an intake leak or vacuum leak. find it by using a can of ether and squirting until engine note changes.

carb cleaner and wd40 don't work anymore.
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Old 04-21-2012, 12:01 PM   #5 (permalink)
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I know that you said you don't have any vacuum leaks, however my old Ranger was doing the same thing and it turned out to be the vacuum hose between the ECM/Catalytic converter and the engine
EDIT: (usually not a place one looks for a vacuum leak).
Once I replaced that ($12) it stopped throwing random misfire codes and idling like it had a performance cam in it. IDK if the Aveo has a similar system, but if it does you might want to look there.
Hope you figure it out. Good luck.
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Last edited by Flakbadger; 04-21-2012 at 12:06 PM..
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Old 04-22-2012, 05:42 AM   #6 (permalink)
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did they unplug the battery when they changed the spark plugs and the valve cover gasket?

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aveo, misfire, p0300, rough idle

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