I have a 92 fox body and I've done a good bit of motor work to it. I have and am still have trouble with the idle when it is raining, moist, and humid outside. I live in Louisiana, so that is probably my first problem. It idles for a few minutes and then becomes erratic and does not want to hold a steady idle. When I try to idle it up, it has a delay like the injectors aren't giving fuel. I have changed the barrometric pressure sensor on the firewall and that didn't help. Any suggestions????

 

My dad had a similar problem in his car. Check you dizzy cap for cracks, and if there are cracks or it has been a while, just replace it anyways. Also, run the car and spray a fine mist of water over the sparkplugs wires and look for arcing. That is where I would start, with the Distributor Cap and the Spark Plug Wires.
Good Luck and let me know if that helped.