1988 buick lesabre idol problems

I need help, cant figure out why it is doing this. when i start the car and it is running in park, once the temperature gauge gets a little above 100
degrees, it starts idling below 10 rpms to about 8-5 rpms, so low that it cuts off unless you keep gas to it.It also does this if i am driving and coming to a stop at a stop light, i have to hold the break pedal and at the same time keep tapping the gas pedal so that it doesnt cut off. i was trying to figure out if the idle needs to be adjusted, but i found the idol screw and adjusted it and it still does this. Does something need to be replaced? Hopefully someone can tell me what to do, thanks, amber.
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Check the iac , may not be working, also clean the throttle body, the base idle screw you turned must be put back to factory settings, this may not be a "dyer: for you.

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