I have an 87 Chevy 1 ton crew cab 4x4 with a 350 TBI. It is idling quite high at about 1100 to 1200 RPM. What can be causing this? Also what are some of the symptoms of a bad fan clutch and also a clogged catalytic converter? Would either one of those possible problems contribute to a high idle? Any input would be greatly appreciated. Thanks.