I don't think you're in the right area for vacuum lines. There should be one that comes in the firewall above and to the right of the inertia switch but it should go towards the heater controls, not the other way towards the PCM. I'd wonder if you have pin fitment issues or a break in the wiring. That would definitely cause a CEL if it's changing the idle. If you find out what CEL you get and correlate it to a specific sensor, then look up a wiring diagram and see what pins/wires you need to be checking, you should hone in on it pretty quick.