All winter truck runs great. soon as the hot weather arrives [ the hotter the more frequent ], the truck will hold at a steady high idle sometimes cruising at 35 mph or above as if I had cruise control [I don't ]. no check engine light, iac changed twice. each time it was changed it seemed fine for about 2 weeks. pvc valve chanced and some vacuum hoses also. want to be ready for this summer . any suggestions?