Toyota 4Runner

Hello: I have a 92 toyota 4runner, 154,721km automatic V6. When I start the truck in the morning, it stumbles for a second then dies, my trick is to wait about 10 to 20 seconds after first attempt then start it again, usually stumbles for a second then seems to smooth out and run fine. It only does this after sitting for more than, say 5-6 hours, once it starts it runs great. I've taken it to two shops who had it connected to their diagnostic machine, both said nothing showed up and I would have to go direct to Toyota. One mechanic did mention a " cold start sensor?&Quot; I did have a head job done on it a couple months ago and I replaced the fuel pump.
Please help, noone seems to know what it is.
March 21, 2007.

Could be the cold start injector-try measuring the resistances of the coolant temperature sensor. How's the fuel filter?

Mar 21, 2007.