Idles too high

the 4.0L engine?
is this engine cold or hot.
why is 2000 rpm wrong for 60mph., (depends on engine and axle size and what gear you were in , then)

the idle speed for hot is too high
did you scan the PCM yet?
if hot , idle is high, is the thermostat holding water temp 180f or above. ? if not that is the problem.

DOES IT IDLE HIGH WHEN HOT?IF IT IS SO THAT'S NOT THE
IACV(IDLE AIR CONTROL VALVE) .

the most probable cause for high idle is the idle air control because this sets idle on todays cars. you could have a vacuum leak, but remove and clean IAC first. to see if it goes to the proper rpms. good-luck !

It sounds like the Idle Air Control Valve is stuck. This will give you a fixed idle it can stick at high idle or low or anywhere in between. If you take off the air cleaner you see where the air is getting sucked into a small slot or hole. spray some carb and choke cleaner in there let it sit for about 5 minutes then start the engine. spray a little at a time with the engine running till the idle comes down by itself. This should take about 2-3 minutes. If it wont come back on its own take the 2 torx screws out and remove it clean with carb and choke cleaner and replace. If it still fails it will need to be replaced. MOST of the time cleaning it will work

Either a vacuum leak or a bad IAC (idle air control valve)

check for vacuum leaks, that will typically cause a high idle.

BUICK RENDEZVOUS IDLES UP REALLY HIGH...WITHOUT PRESSING GAS. WHAT IS THIS?

sound very much like a vacuum leak.... also maybe your timing is off? possibly advanced? try retarding it with the distributor if thats the case...

Look at your air intake on the motor: as the pedal is pushed you'll see the apparatus and a screw that controls how far back the pedal goes when it's not being pushed. The easiest way is to see the idle adjusted and more fixes for the idle problems are available on YouTube and through a Google search.