The most common cause of engine surging (rev up and down) is a dirty air filter.
air conditioning compressors put a load on the engine causing it to slow down, vehicles have an idle compensator which when the air conditioning is on speeds the engine back up to normal idle speed or" compensates" for the added load.
Yes the power steering takes power from the engine if it did not rev up it would make the vehicle shut off due to low idle.
The engine idle may be set to low to compensate for the AC compressor starting up. Rev the engine a few times to see if it stops. If it doesn't, there may be a problem with the AC temperature signal or motor mount.
On a 1994 Buick LaSabre why does the engine continue to rev up while driving even when the brake is applied ? or when driving why doesn't the engine return to idle when the brake is applied? I would check for a vacuum leak
need to check your evap system or you have a blown head
Throttle positioning sensor
The purpose is to control the idle speed, so that you don't idle too high or too low. Look under the engine... you'll see a sort of semicircular piece with a cable attached to it. With the engine running, if you turn that piece, the engine will rev up.
May be your IAC valve (idle air control) they get dirty inside and make your idle act up. Back of the engine toward the passenger side, two bolts and hard to get at.
intake gasket is leaking
check your Idle sensor which is attached to your throttle body. This ussually goes bad and tends to rev the idle up. I had the same problem with my 99 wrangler.
what type of motor is it? the quad 4 or the 2.2