1. Please check the distributor. Take off the upper cover. Inside you can see 3 parts the multiplier, the electronic card and the sensor. The sensor some times is bended out so it is not very close to the rotating part and this provokes instability to the open-close action. Using a scewdriver bend this sensor closer to the rotating part (If you have the distributor out you can turn it using your hand. If the sensor is at the right distance from the rotating part you can fill the magnet that tries to stop the rotation). This problem happens in Toyota 7series often.
2. I dont know if the gas regulator you have is working in compination with the distributor. In 7series I have found two types of gas regulator. Both have two electronic valves on them. In the first case both valves work with the key on (so you can provide + and - using 2 cables from your battery directly to test if the regulator works properly or is a malfanction of the wiring). In the second case the small valve is activated ONLY when the starter/ignition is activated and the big one is activated with the key on and stays on during the truck is working.
3. Check also the water supply through the regulator of gas. Sometimes dirt is collected inside the regulator and the water cannot pass so the gas cannot evaporate.

Thats all I know. Good luck