Q: trouble codes obd po300 po303 po302 po137 need help on 2006 Chevrolet Aveo

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
recently got trouble codes p0300 p0303 p0302 p0137. the car sounds like a hicup at low rpm when at idle or when at idle and i turn on the a/c or put in gear it hicups worse. It runs good when above 10 rpm. I changed the spark plugs they were covered with oil. i replaced valve cover gasket and grommets and now the new ones are staying dry. I put new plug wires on. cleaned throttle body . the codes were erased using obd but the problem still exists and the check engine light hasnt came back on to see if any of the codes that were cleared come back up since i replaced somme things. I dont know where to go from here. The car has been sitting for a week.
(1) Answer
The P0300, p0302, and p0303 codes are all misfire codes, and the p0137 is an HO2S low voltage (or lean) code. It is normal to have a system lean code with misfires. If the car does this consistently, it should be easy to find. Check the coil(s) for corrosion. If you find none, good. Then you need to test the injectors. If you do not have a scan tool that will do an injector balance test, then you should take it to a shop for this. Pull your spark plugs out again and do a simple compression test before worrying about the injectors. If any cylinders have low compression, take to a shop for a cylinder leak down test (unless you have an air compressor and leak down tester). Have you had any overheating problems or white smoke out the tailpipe?