I killed the starter motor in my 4Runner trying to troubleshoot this problem. After I replaced it (lifetime warranty Autozone part) it seems to be starting fine, hot or cold. I also put new NGK plugs in as I had fouled the old Autolites pretty badly messing with it.

I think the plugs made some difference but I noticed also that the new starter turns the engine over more quickly than the old one. I wonder if the engine has to be cranking at a certain speed to make the AFM work properly? I'll have to look into it some more.

I haven't thoroughly tested it yet on a hot day so I'll post if I find anything else out.

Allan