First you have to understand what you're doing by disconnecting stuff. Any time the battery or Engine Computer are disconnected, the computer loses its memory. The fuel metering data will be rebuilt as soon as you start driving, but not "minimum throttle". Until that is relearned, the computer won't know when it has to be in control of idle speed. The engine may not start or stay running unless you hold the accelerator pedal down 1/4", you won't get the nice idle flare-up to 1500 rpm at start-up, and it will tend to stall at stop signs. To meet the conditions needed for the relearn to take place, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals.
Anything that removes power from the Engine Computer also erases any diagnostic fault codes, so you're losing that valuable information. Some fault codes related to no-starts will not set just by cranking the engine. They set while a stalling engine is coasting to a stop. That means the computer may have detected a problem and set a fault code directing you to the circuit that needed further diagnosis, but you erased the codes by disconnecting the battery.
Wednesday, August 19th, 2015 AT 3:49 PM