engine swap over heating

[chris2523]

Your battery has nothing to do with how your car idles

well that isn't entirely true..
if the battery has been unhooked and the computer has been cleared, it won't have an idle strategy and may not idle correctly. and a dead or dying alt/battery can cause enough electrical interference to mess with the car's sensor readings. the same way a bad coil will cause an LS to go into failsafe mode.