I have a strong running 1987 Toyota PU. 22R carb, auto trans, 420,000 miles. About 200,000 on a long block. Anyway, I added 5 gallons of gas from a can to 1/4 tank of gas. The previously strong idle disappeared. At startup, it'll run strong indefinitely on the fast idle from strartup. Even after he strong start and full warmup it'll die instantly with even the smallest tthrottle input. No idle whatsoever. It idled strong before I added the gas. ?????

 

Possible clue: Fast idle at startup doesn't drop. ????