Hi guys so I have a 1991 fc with a 13b n/a. The car starts fine and stay at a high idle of 2500-3000 and stays till I drive it. But once I drive it for about 5 to ten minuets the idle comes down to 800rpms. After it is warmed up I will be driving along and I will go from 5th gear (any gear) to neautral to come to a stop and the car will almost stall out (but doesn’t die). Then once I come to a complete stop the car idles at a low 300rpms. I don’t know what could be causing this.

The car is all stock too. please go easy this was actually really hard to explain in text forum lol.

I have replaced the tps and throttle body. I can’t find any vacuum leaks either.

What should i do next to figure this out?