How do I fix P1516 diagnostic code for 1996 Ford Windstar?

SOURCE: 1996 ford windstar - changing rear wheel bearing passenger side

No on this model they are held in by a nut and cotter pin. You can remove them by hand.

SOURCE: Ford windstar OBD II code P1537/38, P0171 and P0420

It could all be related.P1537/38 are the intake manifold runner controls are stuck open.They are controlled by vacuum solenoids.The P0171 is bank one of the engine is running lean,usually caused by a vacuum leak, P0420 is catalytic converter efficiency code. The computer monitors the switch rate of the front 02 sensors and compares it to the switch rate of the rear 02 sensors to tell if catalytic converter is doing its job. Now if the front 02 is not switching properly then this will cause this test to fail and set this code.
Look on bottom section of the intake manifold at the back of engine(where tranny bolts up) you should see the vacuum motors there on the intake,these are the control motors for the intake manifold runners.Make sure the vacuum lines are hooked up and lines are not leaking. Also you will see a lever from it to intake make sure they move and are not binding.

SOURCE: Find definition for my automitive computer code

Intake Manifold Runner Control Input Error (Bank 1)

SOURCE: 1996 Ford Windstar Instrument Panel Lights not working

Check your fuse in I/P fuse panel #3 5amp fuse for dash lights, also make sure dont have them off by dimmer switch

SOURCE: Engine code p0304 1996 Ford

code P0304 cylinder #4 missfire the test is somewhat long, you did the right thing with the plugs and wires, that is were we would have started also but now that, that did not work it is time to go to work,,,here is the test for the code.....good luck