Im assuming you have the 22RE. The varying rpms at idle could be caused by low coolant level. The rpms will also ocsillate when your foot is on the brake if your idle rpms are set over around 900 rpms. Sorry I cant help with the other issues.

'04 Taco x-cab 3RZ FE stock (daily driver)
'90 x-cab 22RE stock
'82 Hilux 6" lift (ACES HI)
'82 2-Hiluxs' Rally Edition (parts)
'81 Hilux 3" lift (parts/restore)