Need help: Idle goes real low when in gear stopped at a light.

Hey all, hoping someone may have an idea here, before I take it to Toyota for a diagnostic.

It's a 2006 1GR-FE. Started a few years ago, was very infrequent, but lately it's become the norm. My idle, when stepping on the brake, in gear, drops to, according to my Scangauge, around 475rpm. I have an older alternator, a HO 250Amp version that's about 9 years old. Most wiring both pos. and neg. have been updated to 1/0 gauge. Vacuum lines are all original. Throttle body has been replaced. Running an

$360 Optima D27F YellowTop Dual Purpose Sealed AGM Car, Truck and SUV Battery, 830 CCA, Maintenance Free, Versitile Mounting

Optima D27F battery and HBK voltage booster. Stereo has a draw rating of 160Amps. Changed the brake fluid last summer, and it already looks like it could use it again. No hissing around the booster when the pedal is pushed with the engine running that I can tell.

I think that's the relevant info, so if anyone has ideas, that would be great. Thanks.

 

I'd start with checking over the vacuum lines. 14 years on those rubber hoses is a lot.

 

Did you clean your fuel injectors lately?

 

I would suspect a vacuum leak as well. Or a good tune up. Clean TB, maf, pvc, and battery connections

 

Thanks guys. Already cleaned the TB, MAF, injectors, new PCV, so I'll look into the hoses. Probably should have thought of that myself.

 

Grab a can of starting fluid... lightly mist around the questionable vacuum lines while the motor is running. The motor will rev up a bit if any lines are bad.
Good luck.

 

Alright, I told them that the low idle comes when warm, with an electrical load on the motor, heater, lights, etc. The dealership smoked the engine, and all the hoses look good, except for the one from the PCV valve to the intake. 2-3 week wait on that, putting it on myself. They replaced the thermostat last year, and found a crack in the housing, so they're warrantying that work. Does that sound promising? I don't think they checked the idle with a load, because the fan was off when I got my truck back.