My car has about 155,000 miles and it's a Toyota Avalon 2008 V6. A few months ago, my battery died and I got it replaced at AutoZone (by someone who, I found out, wasn't qualified). My car sounded weird after I got my battery replaced and I let the person know it didn't sound right, so he "tested" my alternator and told me that it's actually my alternator that needs to get replaced. I got my alternator replaced by a local mechanic and things have not been the same since. (In hindsight, I should have confirmed that my alternator really did need to get replaced by another person)
Ever since then, my car occasionally started cranking for longer than normal when I would turn it on. I took it to the Toyota dealer and ended up finding out that the person who originally replaced my battery at Autozone put in the wrong battery (I believe it was one that was too small and too weak for what my car needed). I took my car back to Autozone and was able to get the right battery installed, but was still occasionally experiencing longer cranking time when turning on my car. I took it back to Toyota and paid for a diagnostic and they were not able to find any issue besides that my negative battery terminal was not properly tightened (thanks again, Autozone), so they properly connected my battery terminal and gave me back my car.
Unfortunately, the problem persisted but I finally was able to pick up on a pattern. My car does not crank first thing in the morning, but after I drive it around for a while, it takes about 5 seconds to crank before actually starting. Once started, it seems to run fine.
This happens intermittently throughout the day, but if I leave it off for say 8-9 hours, it starts fine again. If I stop the car and start right up within 3-4 minutes, it starts right up without any issues. I'm unsure if this has anything to do with all of the BS I went through with Autozone and my battery/alternator replacement, or if this is unrelated to all of that, but I can't help but correlate the two since my car did not have this problem prior to getting my battery/alternator replaced.
So far I have checked:
Battery (good condition)
Fuel Pump (normal)
Changed spark plugs (installed by Toyota dealer)
Recently changed oil
The problem is still there. Any sensible ideas from experienced mechanics are welcome.