I have a 2000 Corolla CE with 51k miles (bought a couple of months ago).
It ran perfectly during the hot weather (75-80F) and it idles around 650rpm-670rpm. These couple of weeks, there have been very cold weather (60-70F) and it idles mostly around 650rpm but can drop to 630-640rpm. Sometimes, it will suddenly drop to around 612rpm (there will be a very slight shudder) and pick back up to 630rpm. This is with all accessories turned off.
If I turn on the windshield wiper, then everytime it activates, it drops to around 612rpm and picks back up quickly. This only happens during cold weather.
I don’t think it’s the MAF sensor…any idea what it could be?