89 ciera problem with TCC

[jedgxe]

My daughter has a cutlass ciera sl 3.3 v6 160,000 miles.
It has an intermittent prob that I think has to do with the torque converter clutch. When driving at a steady 45mph it will sometimes shudder very harshly. The trans fluid and filter was changed less than 6 months ago and sometimes the car drives without the shudder, therefor I don't think prob is with TCC but rather with whatever controlls it. Only other prob is when engine is cold it idles fine but if you give it any gas when in Park or neutral it will try to die.
Doesn't do that in gear or when warm. The car also had the infamous code 42 which has not returned since I cleaned the anti-freeze from the crank sensor connector cleaned ground connection at c3i module and repaired coolant leak. I am a Mopar guy, so I'm not very familiar with GM engine controlls. What sensors and or controlls have any effect on Torque Converter Clutch and how would I test them ?? is it possible a coolant sensor could be faulty without setting a code ?