Previa - Hard to start when hot outside

[Tom]

Hey All,
This one has me baffled, my 93 Previa has become very difficult to start when the outside temperature is hot, say 80 degrees and above, and the engine is cold (has not been started in say 8 hours). It cranks fine but is will not start (I'm guess fuel related but could be wrong), once it starts it runs great, I can turn it off go in a store and it will restart no problem, when it cooler outside it starts no problem. When this first started if I removed the fuel cap to vent the tank and remove the oil fill cap it would start right up (I'm not sure both of those procedures where needed but that's what I was doing), but lately that doesn't seem to help, so far all I've done is change the fuel filter (didn't help but was time anyhow), any idea? btw no trouble codes or lights.

[TheMAN]

have you tested the coolant sensor?