I’m trying to help out a friend. She has a Mazda 3 2012 with about 134.000. She has over 21 ODB codes, the main ones she gets are: P0304, P2610, U0121, U0155, U0100, U0121. She changes her oil regularly and she had her spark plugs changed about a month ago. Her engine check light comes on, and one of the codes she had was P0304 – Cylinder 4 misfire. She thought it may have been the coil, so she swapped Coil 3 for Coil 4. She had her car scanned again and there was no difference. She has also used fuel injector cleaner, but her engine check light returns. Some days her car runs smoothly, but the other day it was running rough and she had to return home. I’m telling her to cut her losses and sell it for what she can get. Any suggestions and help will be appreciated.