Hi. Unfortunately the car in question doesnt have an air flow meter but a MAP so no air leak here. I now think the judder is caused by the automatic gearbox solenoids sticking. on 3-2 downchange/upchange and only happens at light throttle at about 20mph. and only when hot. The mileage is 206,000 and it would appear the engine isnt the cause. Thanks for your tip re lighter gas. I tried this but no air leaks anywhere.