2004 idles surges
Checked for vacuum leaks, replaced plenum gasket, swappped stepper motor, replaced tps, new fuel pump, all new o2 sensors, new maf. No dash lights or codes. Any thoughts on what's causing this?

 

Have you completed a drive cycle? The adaptations are probably still set to the old parts. When you replace the MAF, 02 sensors, you're supposed to reset the adaptive settings so it goes to the defaults, and once you complete a drive cycle it learns and stores the current setup.

LR T4 used to do it in seconds, but not sure if other scanners like say a commonly found $$$$ Snap-On scanner can.

You could try disconnecting the battery, touching the positive/negative leads on the D2 together and turning on the lights (enough to drain the ECU to default), then reconnect the battery & drive it until you set a drive cycle. 55mph stop n go & some freeway/idling should do it.

I've never really had that issue on any of my personal LR's but I did replace a friends MAF & it wanted to idle at 1,500RPM with the new one. Did the above & it finally went back to normal with zero fault codes.