87 cpe GT 2.3L

[J4KQ4me@aol.com]

Hello all,
         I am a new member of the list, and I have a couple of questions....
First, I have two cars, one is an alpine white 87 cpe Gt (NG engine code) that
has a bit of a perplexing performance problem.  Whether hot or cold, the
engine loses power at different times. It feels like the timing is being
retarded. Now after replacing the fuel dist, injectors, fuel pump, checking
the pressures, repalcing every seal and o ring on the induction system,
cleaning and reparing every electrical connection in the system and doing all
of the pin checks in the bentley manual, i've drawn a blank. It stores no
trouble codes, and it idles too high sometimes. I've checked idle switches,
set the fuel mixture and timing to spec, replaced the lower crank pulley, and
swapped both computers.  In short, I've gone over the whole thing with a fine
toothed comb. Even checked the knock sensor. Ugh. It runs strong, then sort of
bucks, and loses power until you back off the throttle.
 The second quwstion is about my 85 4Kq. The center diff lock doesn't work.
I've checked all of the vacuum lines inside, and they seem good. The switch
makes a sort of leaky sound when it is switched to "1". Are the rotary type
switched prone to failure?   Any help is much appreciated. I am going to
unload the 87 if I can't cure this problem.   Thanks- Jon.