1993 ford ranger stx help?!

Okay so im 17 and my truck is a 1993 ford ranger 4.0 motor automatic 4x4. So recently my truck was making whistling noise but it wasnt loud like i could barely hear it, so i didn't think anything of it but now i dont hear the noise and now my truck idles rough like when i start it it just wants to stall out while idling. It will rev up and down by its self. But if i but it in gear and go down the road it will kinda bog out like loss of power but right after like 15, 25 mph it runs fine until i slow down or come to a complete stop than it will start to idle rough again. I just replaced the fuel filter and it didnt help. There is no check engine light either. So does anyone have an idea what it might be? Thanks

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