I have an intermittent problem with vauxhall zafira?

Zafira 1.6 Club 2001. Intermittent fault garage cannot find it, been on all diagnostics. Any sudden acceleration causes the car to kangaroo and then stop. I had to stop suddenly today and again the car just stopped. Terrible trouble starting again but when does its as if nothing was wrong. Can any one help.
The garage have checked the fuel line and filter but nothing can be found. Great garage, been 4/5 times now any never been charged because they cannot find fault.