rough idle and loss of power
 

i have a 91 ford ranger with the 3.0 V6 that i just bought, the truck had some issues when i bought it but i got a good deal on it and im almost done fixing it up, then i will have a pic up asap. my issue right now is when the engine is cold it will start up right away for about 5 seconds then the idle will drop below 500rpm and the engine will die, i have to hold it at about 2000rpm for about 5 min. for the engine to warm up before it will keep running and after that i dont have any problems except there seems to be a slight loss of power. im thinking its a vacuum leak, but im not sure. any help would be appreciated.