98 2.5L Won't Idle properly

Ok, So my 98 2.5L 5-speed had a cracked head. I just now finished swapping it out and when I started it, it was trying to rev up on its own and was running rough. Before I swapped heads, it would idle normal. Any ideas of what to look at first? I've had a couple of 6-cylinder xj's but this is the only 4-cylinder I've had, so I don't know where to start.

Start pulling spark plug wires while it is running, see if you can ID if one cylinder isn't firing or isn't firing as strong as the others--that would be my start. You could pull the plugs and compare them, but it might not be as clear that way. You can do the same with unplugging the injectors.

if she's "trying to rev UP" I'd suspect a vacuum leak somewhere.

--Re-check the intake-to-cylinder head mounting surfaces for any signs of misalignment.

--verify all vacuum hoses removed have been re-installed.

--inspect all other vacuum hoses for signs of breakage- they are easy to lean
on and break when you're pulling/placing the head from/into the engine bay.

--verify the throttle cable routing is the same as it was- make sure the throttle plate is
completely closed (linkage against the throttle stop) without
any input from the pedal.

Ok, So I got it to run smooth. It was running on 3 cylinders. But I still can't get the idle down. Its idling at 2800rpm. All the vacuum hoses are connected. The check engine code is po123 for the throttle position sensor. So I figured that was why it was idling at 2800, so I checked the sensor and it checked out ok. I tried starting it without the sensor connected and it runs exactly the same. I also tried the sensor out of my other xj and it again ran the same. I'm still thinking its something to do with the wiring for the throttle position sensor, where should I be looking now?

Shorty has given you great advice.

One of the biggest sources of intake leaks, resulting in super high idle RPMs, is not getting the intake correctly seated on the locating dowels OR pinching a wire or vacuum line between the head and intake.

Follow shorty's advice.