Like I said new plugs change the oil is easy in a 318is. go under put a pan drain the oil till its all out. Then seal it back up open the engine bay undo the screw open the top drop in the new filter. close put in high performance synthetic no additive oil and your ready for a good test run. That takes literally 5 minutes to do. spark plugs and wires are almost as easy if it wasnt for the tracks are a real pain in the fucking ass so expect 20 minutes. I dont know about the O2 sensor I'll get back to you on that.
If you dont trust mechanics
take bosseis class or take a course in college or high school if you still attend. I've saved atleast $2000
Actually I save atleast $500 more than most people who own cheap cars and take it to a mechanic. Because once you have your mechanic fix all simple things by the time you pay it off you need to have it done again. Most mechanic in my area order cheap shoddy knock off OEM parts from expensive suppliers then charge you that and charge you $60-$80 an hour and they usually bounce between cars but still charge you for how long it takes t finish the job. So an oil change costs over $200 and you dont know what they did exactly. There also taught to look for problems even creat them so you come back asap. I saw the guy who did a simple check for over heating asked them to add water. I caught them cutting my belt. They said I had to pay I refused I threatened cops they did too. I threatend to call consumer afares they said they'll just change there company name(small gas station namex) finally I grabed the guy with the belt and knife in his hand who was laughing at me put him in an arm lock and held him while he screamed in pain till he offered to do it for free
i know martial arts should not be used that way but they said I had to pay $400 with $200 down payment to fix my car and they said I proabably had to wait 2 weeks before it would be done. They were done in 1/2 an hour and I was gone. I also had them deported