Hey Scotty,

I have a 2002 Toyota 4Runner with around 155k miles on it. I recently had some rust repair work done to the exhaust/ frame where it sat for quite some time and at the end of the work the mechanic said my battery had died and needed to be replaced. I replaced the battery with a new one...

With the new battery installed, I drove the vehicle home and noticed it was going through a "relearning" phase since the battery was disconnected; the idle speed was low and at times the heater fan speed would slow down when stopped at a stoplight in gear. My headlights also dimmed while at a stop, but when I hit the gas pedal the fan speed and lights would increase their intensity.  However even after the relearning phase and with the engine in gear, stationary at 650 RPM, my headlights and fan speed remain slow.

My question to you is this: where do I start with the diagnostics for this issue? Do you suspect these symptoms are indicative of an electrical issue or a byproduct of a lower than normal idle speed? I had the alternator checked (not bench tested) at a few auto parts stores and each store gave me different results. Advanced auto said everything was in working order while the AutoZone test generated faults with my starting system and charging system. The oreiley test also produced faults for the alternator. The alternator belt is in good shape, it doesn't whine and once again when the engine is at a normal operating speed, everything seems to be normal. I only experience abnormalities at a stoplight in gear. I should also mention my engine starts aren't as robust as usual, but it's probably a product of the 30 degree weather and heavier draw on the battery at idle engine speed. 

Thanks for any insight or troubleshooting steps to figure out what I've going on.  

Go Illini!

Brendan McQuillan