I have a 2001 4runner with 150k miles on it. I replaced the alternator 2yrs ago with an 80amp model from Autozone. My truck is idling at 500rpms, the lights and climate fan will increase as the rpms increase. I am having a problem with the battery not charging. I took it to OReilly and they tested the battery which is a 2 yr old optima gel cell battery and said that it is only 45% charged and that my alternator is putting out 11 volts and 30 amps. After searching the forums and wondering if my low idle had anything to do with it I went back to OReilly and tested it again this time with a little higher rpm (1200) they tested the alternator and found it was putting out 13volts and 40 amps.

My question is this.....

Do you think I should look into getting the idle up to 800rpms before looking into the alternator or battery? Or should I replace the alternator / battery again?

This is my first post so please forgive me it this is an elementary question, I apologize. I am just at wits end right now with this truck and dont want to just change out parts.

My thought is that until the idle is up to around 800rpm I cant really verify that the alternator is working, and in turn that the battery is charging?

I do plow occasionally with the truck and was wondering if I should leave the idle where its at and get a smaller pulley on the alternator so it runs at a higher rate.


Is my line of thinking off base?

 

First things first. Start with a new alternator, a real one.

Rockauto will sell you a real Denso alternator for about 120 bucks. Partsgeek will sell you a Denso for about the same money.

 

I went with a brand new alternator and a new battery. Lights and fan aren't dimming or slowing down but the rpm is still around 500.

I ordered a new timing belt seeing my truck has 154k miles on it and 93k since the last belt.

I also picked up throttle body cleaner and mass airflow cleaner

Hopefully that will take care of the problem

 

Check all the vacuum hoses and intake tube for cracks and leaks.
Is the 500 rpm idle all the time or just when the engine is cold? A good cleaning of the IAC valve may help.