Even after trying so many times, I can't tune anything to save my life, nor am I a consistent DS3 racer. The latter is what screws me up most time.
OK. Here we go.
Apply the manumanu tune. Put your abs on 1. And if you're struggling, TC on 1 too. (I use 0)
Accelerate through the gears to the first corner. Coming to the first curb on your left, LET OFF. Coast to the right, and bang on the curb on your right, brake hard and change down all the way to second, pulling the car over to the right to get a wide sweep at the tight double apex.
Don't get impatient on the throttle. In fact don't touch it untill your apexing the second curb. Then get on the throttle (not bang, gradually(still in second gear)). Avoid the curbs if you can.
Accelerate through all the gears with no let offs, untill you approach the 50M brake board, just before the right left at the bottom of the hill. Brake hard, and again change down to second gear, turning the car tight to the curb as you finish your braking. Again, tickle the throttle lightly, and ride the corner round to the next apex/ curb. Use a bit of throttle in between the next 2 corners, then let off again, (still in second) and re-apply the power when you have passed the barrier on your right, and full power for about 2 seconds. ride the long left hander untill you can feel the front of the car begin to understeer. At that point, let off and coast the car round to the second apex point. Use a bit of throttle, and let off again. just like the previous right hander, as you pass the barrier on your right, get back on the throttle and accelerate through up to the large long left hander.
As you approach (the long 180 degree left hander I just mentioned) stay full throttle, all the way to the curb on your right hand side as you enter the kink before the corner. Brake hard bang on the curb, and change down to second gear. Turn it in tightish to the first apex point, and very gently (20/ 30% throttle) ease the car all the way around the corner. Be patient, else you'll lose the rear. When you spot the corner opening out, start to apply slightly more throttle, untill your car is straight, and you can see the exit, then full throttle and accelerate down the hill up to 4th gear before the final chicane.
Your braking point from full throttle, is the 50M board before the zebra crossing. Brake hard on the 50M board down to second gear. It's important you HIT the first curb, and turn your wheels left toward the second curb, but DONT touch it. As soon as you're clear of the second curb, you can accelerate hard through your gears to the finish line.
Now this is no means the FASTEST way to complete the lap. But if you do exactly as I've said, it will be an easy gold.
Good luck