Automatic transmission simulation issue

I noticed an issue with the automatic transmission simulation. When a car with an automatic transmission is held still in drive, it should idle. However, in BeamNG, the engine actually goes below idle RPM and black smoke starts coming out of the exhaust when the brakes are held down. This is likely the result of inaccurate torque converter simulation.

 

There is no real torque converter simulation yet. The transmission was set to slip the clutch so that power is transferred effectively while not stalling the engine. At the time, the engine will push its output to max to increase its rpm to the idle rpm. Thats why smoke comes out.