Car: 2003 Toyota Corolla, 215k miles, manual transmission My auto experience: rudimentary DIY stuff -- oil change, tire rotations, serpentine belt replacement, front struts replaced, brake jobs. I have a nice floor jack and tools. I know very little else about cars. Issue: Only during cold weather, the car idles strangely. I live in Florida, so cold for me (and the car) is something in the 50s or lower. If I've just started the car after it's been sitting a while, it will idle up near ~2,000 for 5 seconds, drop down a bit and then pulse back up to 2,000. It'll do this over and over again for some time. If I've driven somewhere and I park and let it idle, it will often idle very low, the the point where it shakes a bit and feels like it might cut off. It never does, but it seems close. -- A few years ago, after I was quoted over $600 dollars to replace just the front struts, and ended up doing it myself for a fraction of that cost, I decided to start trying to work on my car myself. Looking for advice on where to start to diagnose/fix this problem. The car has been so incredibly dependable that I've been quite complacent with some things. Very little has been done with the engine, fuel system, etc. What I listed at the beginning of the post is nearly all that's ever been done to it. So with that in mind, where should I start? Thanks in advance.