Isuzu: trooper won't hold idle

93 isuzu trooper dohc, with 78k miles, which starts immediately but stalls
immediately.

about one year ago, it would run erratically and once a new fuel pressure regulator
and idle air control sensor was installed, all was well again. fuel filter has been
replaced. once engine warms up, it runs fairly stable for a while but can stall out
when coming to a stop at traffic light when transmission downshifts

this just started happening couple days ago and on the first day when it happened it
had been running absolutely normal the day before. once the problem with stalling
happened upon startup, had to keep one foot on accelerator and keep rpm's up around 1k
to 2k and a large amount of sooty water came from tailpipe. fuel tank was full so am
not sure if there's a connection.

about 6 months ago, the catalytic converted was replaced, new coils, new EGR, new
plugs, new harness

as far as I know, it could only be fuel pump, fuel pressure regulator or mass air flow
sensor. the fuel pump seems ruled out since it runs normally at least for a while once
warm, the FPR seems ruled out since it's only one year old and the trooper 93 does not
have a MAF sensor connected near the air filter

on the other hand, the FPR could be a bad part needing yet another replacement

Gemini Jackson wrote: 

normally immediately on throttle body, ask the local parts shop to show you an image
of the part (Napa has it online) and buy one from Napa or Autozone if you can visually
see same part on throttle (look at their image first on store computer)

if you have one, it's just two small bolts and about 1 minute to replace it, no
special tools needed