idle problems

[mastac73]

i have a 1986 nissan pickup with a z24 in it it is super old i know. i only payied 550 for so you get what you payied for i have a couple of problems one i have a huge rust problem and two it has and over heating problem due to such an high idle i would tell you the rpm's but i dont have a meter so yeah but can tell it is so i plan on replacing my thermostat and and flushing my radiator cause it did have a leak but i fixed that. is there any other suggestions that could fix this or will replacing the thermostat fix it completely