So I've been keeping pretty good care of my 99 gs400 but it seems to have a plethora of odd electrical issues that I can't seem to figure out. The other day I started it up and it seemed like it was about to stall out, yet the battery was fully charged. It eventually started up, so it clearly wasn't dead. After it started up, the car was shaking a lot while idling. The dashboard lights also seem to go on or off at any given moment, and my speedometer seldom works. I've read a post of similar issues stemming from faulty capacitors on the ECU but on the ls models, so I'm not sure how this would translate to the gs. Any thoughts or experiences? Help is much appreciated!

 

Take a voltmeter and verify the output of your alternator.

 

^^^ In addition to that, could be a dead battery thats holding just enough charge only to start the car, but not run it. I had a similar issue a couple of weeks ago, but the car wouldnt start or anything, the car would go dead as soon as I touched the key to the ignition cylinder. Sure the lights in the car were on and everything, but as soon as I touched the cylinder, the sudden jolt of needed power killed everything. I jumped the car and the car ran exactly how you described, I actually had to hold the pedal down to get a decent idle. I was getting 9v of output from the alternator unless I gave it gas to spin it. My alternator is only a few months old and it still acted this way. My battery was just so bad that it was sucking the life out of the alternator trying to quench an ever needing thirst... New battery, everything is great.

 

And check all major grounds and make sure they're good and solid/clean

 

Thanks for all the help. Got the alternator checked and it seems like its pulling power from the battery. Gonna check for any corroded grounds too.

 

I'm just throwing this out there. Have you checked your MAF sensor by your airbox?

My 04GS300 had a dirty sensor and the car randomly shut down temporary while the car was in motion (dash lights all shut off at same time) and would fire right back up. The other thing that led me to the MAF being dirty was that throttle response was really sluggish at times. I initially sent my ECU out thinking it was the capacitor problem you mentioned but that was not the case.

Quick cheap fix was $6 MAF sensor cleaner and about 5 minutes to clean and remount MAF was all it took and electrical/throttle surging problem was gone!! Hope this is of help!!

 

What do you mean " it's pulling power from battery"?
The alternator should be producing power not pulling power.

Sounds like a bad diode in the refractor, time to rebuild or replace.
Good luck...