i have a 302 with 126K miles on it. I found oil in the air box, bad PVC, bad valve body in trans. Cleaned the MAF, throttle body, air box, had trans rebuilt, replaced the IAC valve, made a new battery cable to starter and still have a problem with the idle. Car idles at 1400 in park and neutral, 1000 in drive. Mechanic said the IAC was bad so I replaced it, now he said its the cats cloged, bad O2 sensor and the intake is prone to clogging up with carbon. I dont know what to do. What will cause the idle to stay at 1400/1000? Any help would be great, thanks Jack

Bad o2 would trip the check engine light. A clogged cat would run like crap and choke the car out, easy way to test is to unhook it, ok maybe a pain, easy on the lift. Check the temperature it is running at, it will Idle high in engine warm up mode, and if it never heats up it willl do it all the time. Should run 185F. The next thing would be the pcm, because it controls idle.

Next step wouldn't neccisarily be the PCM....that is an expensive jump to make if you're not sure. Could be as simple as a vacuum leak, letting un metered air into the intake Another way to check the cat is to tap it with a rubber mallot, if it rattles, then the catalist inside has broken apart.....also the temp of the pipe coming out of the cat should be about 10% hotter then the incoming It might be the PCM, but it a lot easier and cheaper to check all the inputs and outputs before you start replaceing the brian of the operation.