Thats ure prob mate - the power steering is draining the power - if you think about it the slower you go, the lower the revs go, so as you break and are say going around a corner very slowly then ure power steering is working off low revs and if your idle valve is slightly buggered then its gonna run outa puff and stall ure engine. Clios are hugely common for it aswel - i should know ive had two that have done it!! A garage can fixed rapidly!!..