My 1990 non-turbo zx has 99k, has been reasonably well taken care of
and has given me very little trouble over the years.  Recently it has
begun to die out at rpm's over 4k.  It acts almost like it is hitting a
rev limiter.  If I let off the gas a bit the rpm's will begin to climb
some, but obviously with less power.  The problem seems to be worse in
higher gears suggesting power might somehow be involved.  If I rev it
with the clutch in, no problem - flies high.  Also - when the RPM's
stop going up - the car stops accelerating (as you would figure!)
however it sounds like something is revving up...  Very strange.  If it
were not for the RPM needle not going up I might think it was
transmission related but it is definitely the engine.  What does this
sound like?  Any change its fuel injectors or something?  Could it be
plugs?  The plugs only have about 30k on them, but it has taken a long
time to put those miles on - maybe they needed cleaned?  Any ideas
would be helpful - thanks!

 Chris.