[ohio1121]

This was my first time ever trying to work on a car, a 1999 SL500.

Before:
-P0301
-P0303
-P0304
-P0300 -Multiple/Random misfire

Work I did:
-Valve Cover Gaskets
-Spark Plugs
-Breather Hoses
-Oil/Filter, Air Filters
-Cleaned MAF Sensor

After:
-All of the 'Before' codes came back

-P0302
-P0130 - O2 sensor circuit malfunction

Note: I deleted the codes with my reader for the first time last night. Prior to that the codes had cleared when I unhooked the battery, is that essentially the same thing as actually deleting them?

The car feels/sounds/smells fine. I'm guessing I need to do the O2 sensor(s)? Is there anything else I should do, maybe the fuel filter? I have to take the car to the shop eventually to replace my shifter bushing bc I don't want to do that myself. I am just trying to get as much done as I can before taking it in.

Thanks

 

[Ruindr]

I would suspect the coil packs if new plugs didn't solve the issue. At least on the M119 later version the coil packs seems not to last forever. It's not that expensive and relatively easy to swap.¨

Did you install the correct spark plugs? You have 16, so I hope so