Thanks RonJ & mk378. Very helpful.

 

When the car idles low in drive or in gear and idles normally in neutral or park and it drives smoothly when accelerating the suspect for the issue is the solenoid on your transmission since 90's models are traditional automatic transmission the torque converter relies on the solenoid to take in electricity when needing power during gears on idle. 90's car with automatic transmission rely on electrical components and air fuel mixture to hava a smooth idle. It is normal for an automatic transmission cars to decrease rpm speed up to 200 when you set an rpm to 900 and decreases to 700 in gear thats ok it is adjusting to the pressure. When it decreases to more than 300 increase your idle speed to 100 to 200 and it will still run ok