1999 GS300 has idle issues

[Anthony]

My buddys car runs great but sometimes when you come to a stop it will die or idle rough.
Always accelerates normally ,and dosn't miss under load ,and overall runs great.
If you put it in gear and put it under load as soon as you let off the gas it will stall.
I was thinking idle air control valve or mass air sensor.
What do yall think?

 

[Trav]

Any CEL?
IAC could be dirty or defective
Dirty throttle body.
Defective TPS
Vacuum leak/cracked vacuum hose or small air leak after the MAF.

A defective MAF would cause more running issues than just stalling at idle.

 

[qdeezie]

Idle air control and TPS come to mind, but when was the last time the fuel filter was replaced?