Yesterday my idle was at 600 when in drive and 1000 when in nuetral. Today I'm coming from work and suddenly my rpms drop to about 100 when in drive, I put it in nuetral and it idles at 500 rpms. I've repalced my alternator, my battery, plugs, plug wires, and O2 sensor all within the last 1000 miles. I have a '87 4Runner, 22RE, and automatic. Any help would be appreciated.