guys, Thanks for the flood of responses.
For those interested in the 1989 suburban 350 4x4 bad running mystery the ANSWER IS...... The EGR valve. The unit was stuck open about 1/4 of it's available travel. When pushed it would move then groan on the way back (it's spring loaded). Occasionally while groaning it would get stuck. None were available here on turkey day so I cleaned it with brake cleaner while exercising the unit. Eventually that worked out the stickiness and it does not groan any more. The vehicle now runs perfect. jg
