I have a 96 explorer that needs a tune up and regular maintence very bad, but my question is that is idels normal at 1000 rpm, then goes low to 500 rpm, then straight back up. it is a constant up and down thing like every half a second, and sometimes it idels so low it dies.

Could be a defect in the ECU. But 1000rpm is not that high my cars normal is 1000rpm. but some older models were about 700rpm
The AC rise is normal. You may want to have a OBD II check by your garage or you can buy a unit to do this. It will scan the sensors fitted for any problems.

You engine is TBI, It uses a MAP sensor check the vacuum line for crack and make sure yo have a good seal, The distributor also check and make sure the pick up does not have corrosion which causes the relutor to stick. As for the EGR it would cause a misfire, and yes the do fail. I am sticking with the IAC as a problem its a stepper motor and has a high failure rate, chack also the ECT (engine coolant temp sensor) for corrosion that gives false reading.

For what I can see you need a tune-up

- spray fuel cleaner into the throttle body directly don't let the rpm drop too much but very close to stall. The engine must be normal temp around thermostat opening.
This part of the job needs to be done with the old spark plugs.

- spark plugs + adjusting gap of the new ones
- compression test.(no more differences between each cylinder +- 25 psi)
- clean throttle body and IAC valve.
Don't forget to change the fuel filter. That should solve your problems.
hope it helps

In general, yes. This is a carb tuning issue. Another possibility is a vacuum leak somewhere, but most likely, it's a carb issue. You'll typically see your rpm drop a bit when you put it in gear, but that it sometimes stalls out points to a carb issue.

You might want to check the air intake. find where the mass airflow sensor is at, usually at the end of the tube that brings in the air throught the air filter. Detach and check the butterfly to see if it is clean. You can buy an inexpensive cleaner and use a screwdriver to help keep open the butterfly so that you can clean just inside the butterfly and in front. This should help.

the only reason for your coolant to go down is that you have a small leak somewhere. check the oil dipstick and see if you have any antifreeze mix with oil, it will have a different color and feel.

Check your air inlet and vacuum hoses for leaks. Make sure the connections are tight. Normally it will be an unmetered air problem.

try a tune up

sounds like the iac motor or the idle air control

That is normal. When you put it in gear, the idle speed drops about 400 rpm.