did you do a diagnostic ? any codes ? just check your earth straps on the engine, there are only three, sounds like somethings loose and causing intermittant fault check the plugs in engine bay for loose connection, pull glove box back and have a look there aswell, just to rule out something silly and causing a fault, Iam no expert but these things can be a simple fix and cause alot of problems Good luck http://dub-se7en.toyotagtturbo.com/useful_info/OTHER_PDFS/4EFTE_4EFE_Engine_Diagnotsic_Code.pdf