Help!!! 90' 300zx engine stall and hesitation

[bigdadddyy]

i have a 90' 300zx na, the engine stalls randomly; mostly on the freeway. also when accelerating the engine boggs down and i have to give it a lot mor rpms to get up and go then it runs fine, and when in 1,2, and 3rd gear it hesitates when i accelerate. i havnt got the closest idea as to being the problem.
plus alot of bulidup of black smog on my bumper above the mufflers

Recent Repairs:
2 new injectors
6 new platnum tipped spark plugs
new MAF sensor
Temp Sensor
New wiring for connections(all through out engine)

Please help with any advise/ info

[Z-owned]

Start here with this and report back to us with what code it kicks out. It could be a few things, what spark plugs did you put in? These car's are pretty picky about the plug type.
http://www.ttzd.com/tech/diagnostictech.html

[t.mcginley.jr]

Did you calibrate your TPS? It could be a number of things, bad O2 sensors, CAS issue, PTU issue, bad knock sensor, etc. Did you check for codes yet?