Engine rpm surges intermitently

you forgot to say hot or cold engine so is 2 answers.
they had 3 engines that year (the nn = liters)
G16, 16valve i4
j20 dohc i4
H27 v6
nobody on earth can guess the engine, and is an engine question
2000 is 100^% normal on any cold engine, 1500 to 2500 range cold
based on coolant temps -30f to 180f.
the colder it is at starter the faster the idle, and is AIC controlled
when hot the engine ecu goes to full hot (normal ) engine rpm controls using the ISC.
the exact parts are not the same on the 3 engine ever.
next time tell engine and if RPM is cold engine or hot.

btw I owned all 3 cars before, so have full documentation on them.
and restored them too. and can field most questions.

Need to take to a shop with a GM tech 2 or higher scan tool. These tools can actually display various sensor readings and voltages in real time and can be used while driving the car to recreate the issue. These are super expensive scan tools so most shops don't have them. Call around or bite the bullet and have a dealer do it. The money you spend on a correct diagnosis will be saved by not throwing random parts at it based on guess work.

run the fault codes and check for faulty MAP/MAF/VAF sensors

tell your mechanic to look up Service Bulletin #96-032 this could fix your problems

Most likely none are related to the computer. Surging idle is often a sign of a vacuum leak and can cause random misfires. Vacuum leak would also cause hesitation. Sensor heater can be a fuse, wiring or bad sensor. What's the window doing?

Have you had a mot or try checking with an mechanic¬!

i would remove the coolant sensors and clean then to obtain the correct reading.

Fill the tank up but do not top off.

Ran the trunk for 15-20 minutes on the highway and recheck the fuel surge condition at 2500 rpm.

If it stop surging then you has a weak fuel pump.

Change the fuel filter will also help.

Also check the fast idle setting.
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If everything checks out then set a smog check appointment in the EARLY MORNING.

Here is the most common cause of surges and stalls, it is the idle speed control air-bypass valve and throttle valve, they get full of gunk over the miles and cause idle issues (stalls) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

That is normal operation. Take the car for a ride and try it then. Zoom Zoom