I just bought a 94 Expo and I have a check engine light on and the codes are:
12 Airflow sensor fault.
13 Intake air temp sensor fault.
25 Barometric (BARO) pressure sensor fault.

I also get blue-white smoke intermittently from the exhaust. I suspected HG and I've tested for combustion gas in the radiator and the test was negative.

Then I looked at the spark plugs and they had oil on them both the part that's inside the cylinder and the outside. I also see oil leak around the valve cover gasket onto the exhaust manifold. So I've changed the gasket and the grommets. Then coincidentally the O-ring for the upper coolant hose on the engine block started leaking anti-freeze, and I've ordered the O-ring. So I haven't had a chance to test drive it to see if the smoke is still there or not.

But do you think the engine codes are caused by a dirty air flow sensor? Thank you!