I have a 95 240sx and heres the symptoms:
1. When in neutral, if I hold rpms constant at 2000 and then rev up quickly,
the car bogs. So the revs go up, bogs at a certain point, then goes up
again.
2. Spark plugs black with fuel - rich
3. Exhaust shoots out black smoke - rich
4. Car runs fine when cold for first 3 minutes or so. Then as the car warms
up, it starts to bog. gets worse at it nears operating temp.
5. While driving the car bogs especially when applying low to mid
throttle. Mostly low throttle. Right when it bogs, if I apply more throttle,
the car seems to regain control and rpms rise smoothly again until it bogs
again. it bogs randomly but around 1000k~3000k rpm.

Heres what ive done so far:
1. Changed spark plugs
2. Switched out spark plug wires
3. Changed rotor and cap – distributor
4. Switched out air intake temp sensor
5. Switched out MAF (4 different ones)
6. Checked intake piping for leaks
7. Checked vacuum lines - ok
8. Tested continuity from sensors (tps,MAF,Intake air temp, coolant temp) to ecu – all ok
9. Changed tps - adjusted it to .5 volts at closed throttle
10. Changed o2 sensor on exhaust manifold
11. Switched out ecu
12. Changed fuel filter
13. Switched out coolant temp sensor
14. Switched out distributor – adjusted timing to 20btdc or last position with timing light.
15. Switched out fuel injectors
16. fuel pressure was fine
17. fuel pump @ 40~45psi = great
18. Removed EGR system so its all gone and plugged up

Things i haven't done yet/worried about:
1. IACV clean
2. TB clean
3. o2 sensor might not be shielded properly? could this be possible? ive read somewhere that the reading could be affected if other signals from a/c or something interfered with it.

What i need is more ideas...cause im running out. This problem popped out of the blue. some things i did before this happened(more clues):
1. went drifting 3 days beforehand
2. when this problem happened, i wasn't the one driving it. it was at a body shop and they wanted to move the car and it just started bogging they said. body work was done on the fenders w/ hood propped up.

please help me out!! just throw ideas out at me. the cars now at a shop but they cant seem to figure it out either..and its the second shop ive taken it to. thanks