At times, not often, my car will start vibrating and giving up like it has no power and does not want to pull, this happens when i am at a stop and it just feels like it is about to completely die on me. And than i would turn it off and turn it back on and it keeps triggering the start sound but will not turn on. I let it rest for about 5 mins to cool off and than it starts up perfectly normal. Also, I have a bad water pump that leaks all my coolant out, thus causing to refill my coolant tank about every 20 miles. Could the water pump be the cause of the car running or the starting? What can it be? Car is a 1992 Lexus sc400.