ls4gs4ownr

I have a 91 Lexus LS400 with 214k miles. Lately, the idle speed in drive, stopped at a light, is about 600 rpm which is causing an irritating vibration. With the AC on, the idle speed jumps to 700 rpm and the vibration goes away. I have cleaned the throttle body and idle speed controller and there was no change. How can I raise the idle speed about 50-100 rpm like it used to be? 2 ways I know - adjust the throttle body stop screw or adjust or replace the TPS. Note - no codes. Please help.