Alright I have a 96 GT that’s completely stock other than a CAI and straight piped off-road x pipe. I’ve had this issue for the past 2 months and cannot figure it out. The car will almost always start up just fine and make it about a block down the road and then as soon as I let off the gas and let the car idle it will start to idle extremely rough almost like it has a cam until the idle settles down and fluctuates from 900-600rpms. I started off rigorously cleaning the IAC valve which seemed to do nothing, I then noticed a coolant leak where the heater hose connects to the intake manifold on the passenger side and decided to replace the entire intake manifold, the car ran fine for about a day and then the issue came back out of nowhere. I took off the fuel filter and saw brown/orange gas coming out of both ends of the filter so I put it back on the car and drove to auto zone and got a new one however the car ran perfectly fine on the way there until I was heading back when it started up again. I let the car sit for about a month and then dropped the gas tank and cleaned it out completely, letting vinegar soak in it for 2 days because I thought there could be rust in the tank. After cleaning the tank I put a new fuel pump and the new fuel filter in and filled up the tank completely. The car ran perfectly fine for about 2 days and then started up the same issue again. I checked the fuel filter again and it’s clear clean gas from both ends. I’ve checked every COP for spark and replaced all the spark plugs, checked for vacuum leaks with starter fluid, checked 02 sensors and still nothing. I have a check engine light but my OBD2 port isn’t getting any power so I can’t read the codes. So far I’m at a loss I’ve been trying to research as much as I can the past few months and I haven’t been able to come up with anything so far.