My 1995 Eldorado ETC will shut down (intermittent) at idle. All electrical power stops. Car does restart in after a couple of minutes. Battery cables are clean and tight.

Testing the electrical system for a parasitic drain on the battery , charging system testing , Main power cables from the battery to fuse boxes . Checking maxi fuse etc...
The BEST Way TO Perform Parasitic Draw Test
Electric Testing Techniques You Need to Know
Voltage Drop Test

Engine stall or RPM fluctuates at idle.

This problem is commonly caused by a dirty automatic idle speed control valve and throttle valve. Buy a can of throttle valve cleaner (do not use carburetor spray cleaner!) from NAPA or Carquest (made by CRC chemicals) and spray it into the air intake while the engine is running, use up about 1/2 the can, engine will try to stall hold the speed up, shut it down and let it soak for 30 minutes, restart and blow out the remaining fluid, shut it down and disconnect the negative battery cable for 5 Min's to reset the base idle control

You may have a defective neutral safety switch. The switch is located on the outside if the transmission case and it is where the cable connects from the shooter inside the car. This covers the no start, the stall is likely due to a dirty throttle valve and idle speed control valve.

Engine stall or RPM fluctuates at idle.

This problem is commonly caused by a dirty automatic idle speed control valve and throttle valve. Buy a can of throttle valve cleaner (do not use carburetor spray cleaner!) from NAPA or Carquest (made by CRC chemicals) and spray it into the air intake while the engine is running, use up about 1/2 the can, engine will try to stall hold the speed up, shut it down and let it soak for 30 minutes, restart and blow out the remaining fluid, shut it down and disconnect the negative battery cable for 5 Min's to reset the base idle control.
Below is a picture of the switch I mentioned.

Try doing the following.

Engine stalling issue at low speeds

This problem is commonly caused by a dirty automatic idle speed control valve and throttle valve. Buy a can of throttle valve cleaner from NAPA or Carquest (made by CRC chemicals) and spray it into the air intake while the engine is running, use up about 1/2 the can, engine will try to stall hold the speed up, shut it down and let it soak for 30 minutes, restart and blow out the remaining fluid, shut it down and disconnect the negative battery cable for 5 Min's to reset the base idle control

The fault is intermittent - strikes without warning - and I guess if there are no error codes - so the fault is beyond the reach of the computer sensors - change your high tension coil.

Check your battery terminal's, check woltage when engine is off on your battery, check voltage when running. Could be alternator, battery ior something wrong with charging system.

when u disconnected the battery u lost the adaptive idle learn program, do the following to clean the intake and allow normal idle

Here are some of the causes of surges, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) 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.

sounds like a battery or ground connection problem , disconnect and clean the inside of the battery cables and the posts,tighter securely . If that doesn't do it remove the other end of the negative cable and clean the cable end and the metal that it bolts to.

ideal situation would be to test for either NO SPARK or NO FUEL at the given moment of no start,Sounds like an electrical intermittant, related to the spark, but what ? Without any failure codes, you have BE THERE, to catch it happen and test. Hope this helps

Here is the most common cause of surges and stalls and low idle, 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.