Runs ragged then picks up? Hijet 2005

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The engine starts fine and idles nicely but when I change up gears it will run ragged for a bit then suddenly pick up! Checking the engine myself I did find a thin hose pipe that worked it's way loose from a connection. I've reattached it but the problem persists. I noted the engine makes a snort gasp sound when I suddenly put down the throttle hard? But not sure if it always has done this? When the engine is badly ragged the engine management light sometimes will briefly flash.

Problem feels like an old fashioned advance and retard vacuum fault. Maybe electrical problem as plays up worse in the wet. I have checked the engine at night time but couldn't see any sparks.

My concern is finding a local (Norwich/Norfolk) good mechanic/diagnostic technician who knows the Hijet. A few years ago I took it for a different fault to a garage who had it for 3 months saying the computer said I needed to change a whole host of things - it ended up being a simple broken spring in the throttle throat. I felt I was paying for the his training! Can someone who knows Daihatsu in East Anglia or anywhere be recommended?

Thanks. Chris