Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
If the miss goes away at a little higher RPM it definitely sounds like a timing issue. Probably too far advanced by one tooth would be my guess.
Do you have and trouble codes other than the misfires?
I'm running through the GM tech sheets-
Have you performed a crank sensor variation relearn with a compatible scan tool?
I've found over 200 articles where GM techs have had the exact thing happen after replacing the engine on the Aveo. All of them were solved by removing the battery cables and holding them together for about 5 minutes then reconnecting the battery and performing a crank sensor variation relearn.
Normally if I find 5 or 6 articles with the same solution it's a pretty safe bet that it will fix the problem.
I would probably reset the adaptives by disconnecting the batter and crossing the cables and then perform the re-learn again. Just don't run it at all before performing the relearn or it will ignore the new relearn values because of the values it pulls on it's own if you drive it at all first.
Sorry, I got pulled out into the shop for a bit there.
Exactly- don't run it for more than a few seconds after the reset without performing the variation relearn.
Sounds good. Let me know how it goes. Other than that The only other explanation I have is timing is off, but you would almost certainly get a check engine light if that was the case.
Sorry for the delay. I was out all weekend.
A bad O2 sensor could cause a misfire if it is trying to lean out the fuel trims or even if it is trying to make it too rich. Do you have a scan tool that will pull fuel trim data?
That could be slightly rich, but all cars and engine temps are different, so it's easiest (for me anyway) to look at the fuel trim. Negative trim means it thinks it's running rich and it is trying to lean out. Positive trim means it thinks it's lean and is trying to rich it up. Anything above about 5% at an idle is out of the norm.
It's best to check at operating temp. The fuel trims might be in the negative because the engine isn't warmed up and combustion isn't as good when it's cold.