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Jared D
Jared D, ASE Certified Technician
Category: Chevy
Satisfied Customers: 1218
Experience:  Shop Supervisor at County Fleet
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I have a 2004 Aveo that runs rough and I can see on my

Customer Question

I have a 2004 Aveo that runs rough and I can see on my scanner it has misfires on all the cylinders
JA: How many miles are on the car? Is it a steady misfire? Or random?
Customer: Just put a new motor in with 90k. Its a random miss. I have changed the plugs, wires, coil pack, checked the timing and swapped the injectors. Compression is 165-175 in all 4 cylinders
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: Have tried everything with no help. It seems to go away when I raise the idle to about 1200 rpm
JA: Anything else you think the mechanic should know?
Customer: No I think I listed everything I tried so far. I dont hear a vacum leak but have not yet sprayed cleaner to find one
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Chevy Mechanic about your situation and then connect you two.
Submitted: 3 months ago.
Category: Chevy
Expert:  Jared D replied 3 months ago.

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?

Customer: replied 3 months ago.
No other trouble codes
Expert:  Jared D replied 3 months ago.

I'm running through the GM tech sheets-

Have you performed a crank sensor variation relearn with a compatible scan tool?

Customer: replied 3 months ago.
I did the relearn and it did not help
Expert:  Jared D replied 3 months ago.

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.

Customer: replied 3 months ago.
after crossing the cables, I should not start the car untill Im ready for the relearn procedure?
Expert:  Jared D replied 3 months ago.

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.

Customer: replied 3 months ago.
Ok I will try that tomorrow night after work and let you know what happens. Thank you for your time
Expert:  Jared D replied 3 months ago.

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.

Customer: replied 3 months ago.
I tried the relearn last night and it still has missfires. While driving it I did get a new code. P0137 downstream 02 activity. Can a bad downstream 02 cause the missfires?
Expert:  Jared D replied 3 months ago.

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?

Customer: replied 3 months ago.
I do. I was watching the 02 and it would go between 550-650 counts. Which indicates a slighty rich condition, correct? I did not look at fuel trim data. Will try that tomorrow
Expert:  Jared D replied 3 months ago.

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.

Customer: replied 3 months ago.
Ok i will look at trim data tomorrow and see what it says. Is the 5% rule once the car reaches operating temp?
Expert:  Jared D replied 3 months ago.

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.