im getting all 4 of these codes now.. I had the 171 and 174 for sometime and cant find the issue to save my life. I checked the vac leaks and exhaust leaks with no luck at all. While out yesterday I floored the truck a few times to see if the issue had gone away and then popped the 131 and 151 code along with the other 2 again. I pulled the intake off tonight to che k the intake gaskets but those look fine. Im still replacing them just to be safe while its off. Any other ideas?? MAF is spotless also