Shudder & Stop


I bought a 1999 Daihatsu Terios + in August 2004. I drive about 35 miles every day to work and get caught up in heavy traffic, I started to notice last summer that when moving slowly in traffic my car would sometimes shudder and shake and cut out but would restart again no problem. I put it down to the car overheating and didn't worry too much about it as it only happened in heavy traffic. Since November 2005 the car now shudders and shakes and cuts out when I am driving, especially if I am slowing down at a junction or going round a roundabout. It cuts out & stops, I have no steering until I re-start it and it is extremely dangerous. Does anyone have a similar problem or have any suggestions as to what I can do to try and fix it as my car mechanic is baffled. I am also half way through my finance agreement and have no mission of ever selling it the way it runs and I am probably going to cause a serious accident. PLEASE HELP!! THANKS.