The other night while I was driving my recently acquired 89 van 2wd the check engine light came on for a few minutes and then went away. Hasnt been back on since but I was curious to check the codes and I found that I get 2 blinks 5 blinks and then 6 blinks

2- air flow meter?

5- oxygen sensor? (I am getting bad gas mileage so I wonder 18-19mpg)

6- RPM signal?