help is appreciated. 93' wont idle

[94eezye]

She starts up just fine but after just a minute of idling she starts sputtering and losing power and the oil pressure gauge starts ticking and goes to zero. Once you give her some gas the pressure goes back up. Same with driving her. She drives fine until you stop, it starts losing oil pressure again till you get back on the gas. It acts like its not running on full power either. Im new to the 4.0 motors. Where should i start?