Check engine light

I have a 1996 Jeep Grand Cherokee Laredo, V-6. Sometimes it starts and the rpms come up then they immidiately drop and the car dies. Always starts on 2nd try. Then the check engine light is always on. Feels like it is runing rough at cruising rpm of about 1900-2300 rpm. And then, when I get to about 2500 to 3000 rpm the check engine light begins to blink. When rpms come back down the light becomes steady again. When I am idling in drive, like stopped at a stop light or stop sign, sometimes the rpm is erratic and sometimes the car dies. Thought it was a fuel problem, check all lines, and changed the filter, still no change. Any ideas would be appreciated. Oh and don't know if this is related or not, not sometimes when I start the vehicle, the gas gauge reads empty, but I know there is gas in the tank. Everytime this happens I simply shut the car off and restart it. Also, again don't know if its related, there is a computer of some sort under the back left seat that gets hot to the touch when vehicle is running.