poor perfofmance

[SUPRASHANE]

I have a 1990 2.5 twin turbo limited edition automatic targa top with the revs increasing and degreasing in idle. when you select drive the revs drop but the acceloration is rising and falling as you are driving. i can also get the revs to drop if i remove one of the vacume pipes going to a sensor at the back of the engine.

can any one suggest where i might start looking. also can any one suggest where i could get a diagnostic reader for the fault codes ??