I JUST PUT A USED ENGINE IN MY TOYOTA THE ENGINE RUNS RLY GOOD BUT THE TRUCK HAD BEEN SITTING FOR ABOUT 1YR EVERYTHING IS CONNECTED RIGHT BUT WHAT WOULD CAUSE MY CHECK ENGINE LIGHT TO COME ON IT WHEN I START DRIVING IT DOESNT COME ON WHEN I CRANK MY TRUCK UP ONLY WHEN I TAKE OFF?
cars are like houses, if you leave them in a dormant state for a long period of time, things tend not to always work. I'd go have a shop diagnose it, or pick up a Haynes manual and do some trouble shooting.
sounds like speed sensor either not working properly or connecters need cleaned
Buy a haynes manual and look up diagnostics. It should show you a plug that you need to disconnect and put a piece of wire from one hole in the plug to another. Crank the truck and count the flashes of the engine light, the find the diagnostic codes in the book, then go from there.