I have a EF XR6 6 cylder which has a miss/backfire from idle only and it doesn't happen all the time, If I take off with over 1500 RPM, It is ok, just hesitates a little. . If I am gentle with it, it misses and sometimes backfires.
So far have replaced, leads, plugs, coil, fuel pump,filter, & injectors. TPS and IAC. The car has no fault codes.
Any ideas what else could cause this?

Possibly a vacuum leak somewhere around intake manifold.

Try tightening exhaust and inlet manifold bolts first(unmetered air causing bad/poor idle). Put a multimeter on the 02 senor and makesure it's swicthing between 0.8v-0.1v. If it's favouring 0.1v-0.4v(lean) or 0.5V-0.8V(rich). If the bolts are tight I would be looking at the ECU,

Take the ECU apart and check the the earth rail continuity and the 2 lugs that earth to PCB to ECU casing. Also check the capacitors haven't popped.

Do a search- EF ECU's are common for the idle drive cct to fail.

check compression--sounds like head leak-when revs are up higher comp & faster rate of fireing can overcomes symptoms

What EL_Fairmont said..

i chased an intermittant miss in my old ef xr6 wagon for a couple of years. long story short, what finally fixed it was the cam angle sensor. i had it in at a couple of ford places to check fault codes on a number of occasions over the period but always came up clean. i have a mate who is a auto electrician and has the equipment to check codes also and his picked up the cam angle sensor.

replaced with a second hand one and all was good.

not saying that your problem but something else to think about.