Ok i know this is a popular subject but i cant ever find a solid answer or advice. I replaced my plenum but before that even the truck idles with a miss. Now after the repair its hard to start sort of but will start and idle but now backfires out the tailpipe and idle rough. I've sprayed around for a vacuum leak but no luck. I've heard of the IAC (cleaned mine) and o2 sensor and everything else. Which is more likely to be? I've rerouted my plug wires and they all check out ok as well as firing order new wires and plugs as well. Any suggestions?