First I'd like to say hi to everyone here. Not really a car forum guy in the past so kind of nervous for a first post.
My 03 galant has been having this symptom for a while. The idle rpm is too low (<500) and sometimes can stall when braking. By far I only tried a few things that easy to do. Cleaned MAF sensor, throttle body and IAC valve. Seems only helped for the first time but not now. Never see the engine light one making it harder to diagnose. When it was colder i actually noticed the idle rpm go up and down periodically. When the rpm drops to ~500 it will bounce back to ~2000 as if I was hitting the gas (while actually i didn't) .
Was thinking about vacuum leak, haven't tried testing though. Just wondering due to the age of this vehicle, how likely that this is caused by old spark plug, fuel filter, fuel injector, etc. Or could it be something more serious. Any input is appreciated!