Why won't my 1984 crown victoria hold it's idle?

Possibly dirty/faulty idle air control valve or dirty throttle plate. Could also be egr or pcv valve sticking open.

the car is 30 years old- the engine is 30 years old- the carb is also 30- try adjusting it- try rebuilding it- try replacing it-

I would look for a vacuum leak at the intake manifold - where the manifold meets the heads as well as at the EGR and check the PCV. Your engine is Throttle-body injected so there isn't an IAC and the Throttle plates are constantly washed by fuel spray. There is an Idle Actuator (plunger- type device). It's a small stepper motor with a button on the end of it to tell the EEC-III PCM when the throttle is at idle. Yours is a difficult system to diagnose and even more difficult to find someone that knows how to work on it. While I was factory trained on this system in 1988, I avoid it as much as possible. There are no trouble codes, it's a 9 volt system and all electronic diags are performed with a Breakout Box and Volt meter.

Thanks for the tips I will try looking into this. Also, I've found out that the arrow indicator for the transmission on the dashboard is somehow dephased so I might have been on the overdrive lock which I think would explain the engine dying down when I don't give it gas.

I changed the egr value and fixed several problems..