Hi Dolande
I bought one of these for a race series and also found it very impractical to drive due to the immense lift-off oversteer.
As I was running in a Un-modified Cars series I didn't have the luxury of playing around with a racing suspension, so I simply tweaked up the ASM from zero until the car behaved under braking.
There are ways of preventing such poor suspension behaviour but the essence of them is that you strive to control the weight coming off the rear axle so that the back end doesn't become suddenly light.
This would mean such things as stiffening the rear springs along the lines of assuming a 40/60 weight distribution (i.e. make the rear much stiffer) and stiffening the Rear Rebound.
You could also try increasing the Rear Camber somewhat or running stickier tyres on the rear but I'd recommend you played around with the springs and dampers first.
One oddity that I noticed with dialing in a Lotus Elise 190 is that, for light MR cars, the game seems to make the front suspension geometry 'spring back' on corner exit (having the effect of giving you opposite lock when you really don't want it). The counter to this I found was to have the Front Stabaliser very soft (2) and the Rear very stiff (6) - that did the trick.
As a final desperation measure if nothing else works (and you don't want to use too much ASM) try fitting a Roll cage. That straightened out an SL500 I was having real stability troubles with on the Nurburgring.
Sorry to be so vague but I'm at work at the moment so I have no access to my notes or opportunity to experiment in-game. I hope that some of this helps anyhow. Good luck.