my father has a 90 dakota with a 2.5l engine. it was a freebee and the only thing that was changed was the oil and the egr valve, and the engine rattles,it sounds like valve rattle and the throwout bearing makes noise. it rattles more when you let off the gas and now that we changed the egr valve it has more power and will idle with all the hoses hooked up. someone told me the oil orifaces in the head get gummed up and starve the valves is that true? is there a shop manual i could download for free,dad is poor or cheap.