When I start or shut off my 1997 Riviera the radio antenna sounds like it should go up and go down but it doesn't. The antenna motor shuts off as if it is working...what part should I replace

Try and clean the entire motor and antenna setup.

Your flywheel may have broke or the crank could have broke. If the crank broke the engine is done. Try to turn the engine over by hand. You can put a socket on the crank pully bolt and try to turn it.make sure the key is off and out of the ignition. Sorry for your loss.

If it's an electric antenna, it should retract when you turn the radio off. If not either the relay or the drive motor has failed. if its a "fixed" antenna, you don't do anything and just leave it in place.

there is a resistior on the heater box on fire wall it burns out to cause that to happen it is located you will see a 3 plug wire connector the resitior has 2 screws that holds it in

Does have a power antennna,noise should repeat if you turn the radio off then back on.

I assume that the power antenna unit is an original equipment unit, if so.
1. Does it run for about a minute then stop? If this is the case, your antenna shaft needs to be replaced. This is a very simple procedure that your local radio install shop can do for you in about 20 minutes.
2. If the motor never shuts off as long as the key is on, you probably have a defective relay on the antenna motor. At this point you need to replace the entire unit. A job that can be a bit pricey because of the price of the unit itself. A cheeper fix is to replace the power antenna with a manually telescopic unit, (no motor), or a fixed unit, (doesn't go down). If you opt for the latter, remember to unscrew or lower the antenna in automatic car washes!

You need to pull the fuse for the antenna or just unplug it. It has a fairly ridgid plastic wire that pushes the antenna up and down. Works fine until the wire breaks then it rolls up (antenna down) but it never increases resistance because the antenna never comes down , it's like a fishing reel when the lure breaks off, so the motor thinks that the antenna is still coming down and it will run and run and run trying to do it's job. Your lucky it stuck up and not down. If you want your antenna to go up and down again you'll have to buy and install a new one.

your blower motor has gone bad and it over heats and shuts down

Fault in the retractor assy. Is the mast bent. If it is gently try to straighten best possible lube with silicone spray. With someone turn off the radio , try manually putting antenna down with the palm of your hand squezzed around mast and forcing. Do the same going up, pull by the end tip ,

sounds like if u have an alarm system that it is engaged while you are trying to start the vehicle causein shut down of ignition and or a bad chip in your key