We have had a jerkiness/misfire problem on our 2008 Opel Zafira 1.8i. It happens at just the point the throttle is opening, i.e just as you have resistance on the accelerator. It’s particularly noticeable when you want to just keep the car moving in, say, a 30mph area. The car jerks quite badly at times. If you accelerate it's fine, if you come off the accelerator it's fine. It’s just that bit in the middle. I've tried the main Vauxhall dealer but they couldn’t offer any solutions and I've tried a mobile tuning service.