1996 Ls 400 Idling question ?

[LS400Head]

My 1996 LS400 - When my car is running at Idle The RPMS go up and down up and down. before this was Happeinning my car ran like silk

Do I need a new Timing Belt ? 175,000 miles

 

[Lextreme II]

Possible ISC

 

[LS400Head]

question

what is ISC ?


Thanks for your time

 

[Thermactor]

what is ISC ?


Thanks for your time

It's the idle speed control valve.
Back when I owned a Supra, oscillating idle could have also been caused by a bad throttle position sensor, so that's worth checking out as well.