The engine rpms are so low the car stalls. Why and how do I fix it?
replaced battery on 2003 Lexus ES300
Make sure you did not accidentally pull one of the vacume hoses off your Air Breather during your battery replacement. It also would not hurt to go and buy a couple of Cans of Sea Foam engine treatment and pour one can per full tank of Gas for a couple of fill-ups. this will clean your injectors and Valves. Sea Foam has proven to work very very well on my Lexus you will notice your Fuel economy to increase.
This happened after you replaced the battery? Make sure you didn't disturb any electrical connectors around the battery area.