Just thought Iíd post this to give someone else having this problem something to check before they go pay tons of money fixing something that cost me nearly nothing. I bought an Ď10 Aveo LT for my wife in November with a little over 100K miles on it. She does a paper route for a job and almost immediately started complaining the gas mileage was bad. I calculated it at about 18 but didnít think much of it, considering she never gets above 25 mph working, it was super cold out, and she loves to put the crappy cheap ethanol 7/11 gas in it. Then she says it stinks like rotten eggs, which Iíve read was common with Aveos, and she was right it was overpowering at idle once the car was warmed to temp. CEL started coming on in February for misfires in cylinder 4, sometimes cylinder 2 and then finally all cylinders. It would come and go. Pulled the coil pack and pulled the plugs, they were platinum plugs and in rough shape so replaced them with regular copper plugs. Here is where I messed up - didnít do my research on the gap.. the plugs in the car were gapped at .44 or so and I just assumed that was correct and installed the new plugs with the same gap. A week goes by and her gas mileage was still bad, eggs smell got worse and the car actually went into limp mode. She takes the car to a shop and they tell her the catalytic converter is bad and want $1500 to do it. I said no way bring it home. Did some more research and found the gap should actually be .31. Pulled it apart and brought the gaps down... runs PERFECT! No more smell, mpgs average 24 for all city driving, no more hesitation and CEL went off and stayed off. 4 copper plugs for $12 and the right gap was all it took. Just thought Iíd put this out there for those with similar issues before you start worrying about the cat or tearing apart the throttle body or injectors and get charged out the ass by a shop and still not get it fixed right.
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