Toyota Tacoma won't start when hot?

What would cause your 96 Toyota Tacoma to not start ONLY when the engine is hot and it's a hot day?

• Answer:

  This is a known problem with the Tacoma's. I have a 95 with the same problem. The issue appears to be called the heat soak issue. I changed the EFI relay, intake air temperature sending unit, cleaned the MAF, no change. The last thing I did was change the thermostat to a Stant 48457 which is 170 degrees and appears to fit perfectly. I did this because I noticed that the water thermal sending unit was showing a spike of up to 25 degrees on a hot day after the vehicle was shut down. I would shut it down at 191 degrees and it should spike to 216. With the new thermostat, I am spiking only to 190 degrees so far and the vehicle is starting ok. However, I need more time to verify that this fixes the issue. There are those out there that say the issue is leaky injectors, fuel pressure regulator, idle air control valve, etc. I took the truck in to a mechanic and he could not even get the truck to show the symptoms. I believe the idle air control valve is ok because the engine idles higher when the vehicle is cooler indicating that the idle air control valve is receiving the signal from the ECU to add air when the engine is not warmed up. You can disconnect the intake air temperature sending unit to get the vehicle started in the summer but it will run richer and your mpg could suffer a tiny bit although I have not noticed any issues when I have the IAT disconnected except a check engine light because a circuit is opened. I use a PLX Kiwi on the dashboard hooked up to the OBD II diagnostic plug to get the water thermal sending unit measurements.