I have a 1995 suzuki sidekick that is revving hi then low while in nuetral also when driving now it revvs up very high while sitting at a stoplight

At what RPM?,sure the 2wd has no tachometer,

Sidekick, with what engine? sure 5speed and 2wd,
but what engine.?
in 1995 they (last year this) 2 engines
the 8v and 16valve,
both, night and day different, EFI.
TBI and MPI injected, 8v is black top, 16v says 16 valves on top.
but both engines, will fail ISC controls like that if there are problems.(idle speed controls)
the surging (hunting) is one of 2 things.

1. (too lean, or air leaks)
2. or ISC lost control)
   

the ECU on the car will in fact hunt the ISC if it can not attain
800 RPM hot IDLE, that is its JOB, to do that, endlessly.
in fact 200 times a second.!
but is not working. (this control, its out of control for sure)
to find this can be easy or hard.? (luck and true causes)
depends on true cause.
I cant do both engines here, be like 10 pages.
The 8v engine races with all air leaks. and hunts. (races)
the 16v goes lean with all air leaks, (air density system is unique)
and goes slower, RPM and may hunt. no RPM stated so cant wax smarter...sorry.

so its a dirty ISC? cant close fully, ? clean it? first.
the 8v has air leaks. caused by vast reasons.
cracked hoses. leaking diaphragms, even the brake booster can leak. lots of leakage patch possible
or some one fiddled the idle air bleed screw making it fail.
try closing that valve (screw) turn it CW directly clock wise.

this page covers both systems.

http://www.fixkick.com/fresh-air/idle-air-supply.html


this ISC cleans just like the EGR that leaks.
egr leaking cause, low RPm and it too, can make the ISC go nuts.
so, but no RPM stated. so.....
eg: hunting from 1000 to 1500RPM
or hunting from 500 to 700 rpm?

i pinch all hoses first.
if RPM drops the hose is cracked or the other end is leaking air.
every 50k miles?

http://www.fixkick.com/sensors/cleaning-egr-isc/double-trouble1w.JPG

does RPM go below 800 RPM HOT engine?
yes ./no
this a is key factor.