Does the 1990 4.5L have the EGR tubes referred to in previous post? If not, what is the procedure for cleaning it?

Yes. Remove aircleaner. Hold throttle blades wide open and look down the throttle bores with a strong light. The tubes sticking up at you (below the throttle plates) from the floor of the intake manifold are the EGR tubes. Use a piece of stiff wire to rod the deposits out of them all the way thru down to the passage below. Simple and easy.