My car does not idle!!!

I have a Ford Sierra Sapphire 1.8 CVH, it will not idle at all and just cuts off. It has done about 17,000 miles. But a few days ago when I put some engine flush in it to clean it out, after running it for 15 minutes It let you idle for the whole nite after it. But then the next day when I started it up it wouldnt let me idle again. I put a new timing belt on, changed the oil and put a new oil filter on. Does anyone know what it could be????