I'd bet on the fuel relay. My guess is cracked solder joints. Take out relay... take off cover and examine the back of the circuit board with a magnifying glass. Chances are you will see a circular crack around one or more of the solder spots where pins from the electromagnet and points that are mounted to the other side of the board, stick through to the back of the board.
If so resolder the spots or buy new relay from parts shop.
1993 190E 2.3
2000 Toyota 4x4 Tundra