my friends ls has this problem that when his car has been warmed up for at least 45 min and hes driving in the freeway and his tempreature gauge goes to cold and his idle goes to like almost 2k rpm's or sometimes 1100 if the needles not all the way towards the cold side. what could be the problem. i want to find out what he needs to get to fix it

 

has he changed anything to his coolant system? an aftermarket thermoswitch? anything of that sort?

 

sounds like a temp. sensor acting up....mine did when i ran out of coolant

 

Thermostat?

High idle sounds like maybe a problem with the IACV or FITV(do LS' even have them?)

 

no he hasnt changed anything im thinking its the termostat