2005 Volvo V50 T5 M66
Hello I recently got a V50 for cheap but I didn't know the state of the car or anything, other than the car looked like it has been taken care of with nothing broken and all original paperwork including sales sticker there. The car had a P0300 code along with P0301, P0303, P0304. The autozone OBD scam said that it believed it's an issue with the ECM and that it needs to be replaced, however I highly doubt this because everything else works great. I changed all the spark plugs to OE ones and moved the coil from cylinder 2 to 1 and from cylinder 5 to 4. After about 20 miles of driving the check engine flashed and went away and when I got home I scanned the car and got the P0300 and P0301, P0303 codes again but the CEL is gone. What should I look at next? Also for some background info I drove the car back like this from AZ to CA with no issue except that only once I got the flashing red triangle with Anti-Skid unavailable and Brake Failure message I pulled over turned the car off for 5 minutes and when I turned it back on it was perfect.