1987 Pthfinder

1987 Nissan VG30i in Pathfinder.
newly rebuilt from previous running engine.
Replaced block and fresh heads used original working components.
I did all the work described below.

Freshly installed vacuum hoses. 
New fuel pump.  
throttle body recently disassembled and cleaned .
Cleaned two idle solenoids, 
injectors. throttle position sensor and wiring
Compression good.  
Charcoal can and vacuum motors good.
Electrical connections all good.
Compression good. 
Triple checked the timing belt!

Post rebuild start up yielded  these symptoms:

Engine rpm fluctuates ~600 to 1200 rpm in a ~3 second cycle, 
as if pressing gas ped then releasing; steady up then drop.
Grey smoke. Plugs get sooty.
Key on engine off: fuel pressure goes to about 36 (correct). 
Engine running: pressure fluctuates with rpm
Pressing gas (as if to rev) engine bogs and stalls.
Unable to set the distributor timing.

Can almost control fluctuation with hand over TBI intake.

No ECU error code (44).

Could this be a bad fuel pressure regulator? 
Some internal leak in the throttle body?

Been trying to figure this out for months!
Please Help and many thanks.
Curtis in Austin