I've got a 92 3.0 4x4 w/ 55k miles with a rough idle. Sometime it feels like a constant mild stumble and other times it's more of an intermittent miss, and it feels stronger when the revs are dropping after blipping the throttle.

Tach is rock solid at 700rpm, ignition and cam timing are confirmed correct. Ignition timing does bounce around a bit due to the stumble/miss.

For maintenance I've done plugs/wires, cap/rotor, coil, and 02 sensor, fuel filter, run a bottle of Techron fuel system cleaner and seafoam separately. As well as timing belt, all new fluids and MFI relay.

I've sprayed brake clean on every vac hose and fitting with no results, and pressing the brake pedal has no effect on idle, so I'm pretty sure it's not a vac leak. No egr from factory, but PCV, etc have been removed.

No check engine light, diagnostic port shows Normal. I do have the ABS light on, but the diagnostic port doesn't give me any reading on those pins.

Things I haven't done: pulled the injectors, tested the IAC valve (truck runs at 1100 rpm with it disconnected), pulled the ECM (which was replaced by the PO), or cleaned the air intake sensor, I've read mixed reviews about using MAF cleaner on them.

Any ideas?