A common concern DIY Toyota and Lexus owners call CARspec for is a rough idle, starting and dying, or a hard start just after replacing or disconnecting the 12 volt starting battery. We wrote about something similar on the Prius, being a common cause of the MIL.
When the starting battery is disconnected on late model Toyota and Lexus vehicles the engine control module loses the learned position of the idle air control valve or throttle actuator motor (throttle-by-cable or throttle-by-wire, respectively). Any buildup on the throttle bore or butterfly valve will reduce airflow through the throttle (now sitting at it’s default position), causing the roughness or hard start. The higher the mileage the more severe the condition. The repair? Clean the throttle of junk buildup and it’ll run significantly smoother. Post cleanup it’ll idle higher than normal for a bit, settling back down once it learns the idle position again. CARspec recommends using traditional carb cleaner to clear the buildup – we use a modified hummingbird feeder cleaner to reach all parts of the bore. You can check that out here in our article about replacing a Prius’s 12 volt battery.
Here’s a DIY from YouTube demonstrating his procedure for cleaning the throttle on a 2003, 2AZ powered Camry:
As Eden Prairie and Chanhassen’s Toyota and Lexus repair specialist we hope this helps the DIY and professional auto mechanic alike sort out the typical rough idle after a Toyota or Lexus battery replacement, repair, or disconnect.
