I had the exact same problem with my 1996 Tacoma, and took it to the dealer three times. Spent a lot of money before I took it to a friend who had a sensor troubleshooting device. The troubleshooting code did nothing to help our search. Finally...we found a sensor, just past the air filter intake. This "sensor", whatever it is, had two small wires and was covered in "junk". The problem was that I had installed a K&N air filter a few months before, and the oil used on the air filter had gotten past and allowed these two sensor wires to pick up all sorts of debris. Cleaned the sensor off with a little contact cleaner in my garage, and I have never had the problem since (over two years). Try to find and clean this sensor first. Just past the air filter intake. Good Luck