1987 sedan deville stalls under load

I have a 1987 sedan deville with the 4.1 engine, and it tends to stall under load. One day as exiting the freeway and slowing down to a stop the engine acted like it was going to stall. Then a couple of miles later as making a right hand turn the engine stalled. At first the check engine light came on and said the o2 sensor was bad. Replaced it and the light never came on again but still am having the same problem.
After a few trial and errors and a replacement of the idle control motor, I have found a way to reproduce the stalling incident every time. With the car warmed up and shifted into drive if i move the wheel to the extreme right or left kinda fast, the car stalls. But if i move the wheel slowly and allow the car to even out its idle and when I am at either extreme right or left and i turn the air conditioning on, as soon as the clutch kicks in the car stalls.
I first thought it was the idle control motor was not compinsating enough for the excess power drain but the engine idle does seem to go up a . I was monitering the idle in the cadilllac's diagnosstic mode.

Oh and one more thing. The car was bought used a few months ago and now looking into the radiator, it looks kinda gunky and dirty inside. Also when the dipstick is removed the oil looks a little thin and watery. So one posibility could maybe be a blown head gasket. I'd appreciate any help with my problem, thank you.

Cam shafts were a common problem on that engine your symptoms can be caused by a bad cam. What happens is engine power at low speed is down and the isc cannot compensate quick enough to keep the idle stable. Recheck your codes and see if code 30 is in there that usually points to a bad isc, but it also is triggered by the isc not being able to maintain a stable idle. All this assumes the throttle body is clean and the engine tuned and timed properly. If the HD gasket was bad you'd have coolant loss.