Isuzu Piazza (impulse in US) 2Ltr turbo which has a loss of power?

I have a isuzu piazza turbo, it has been stored for 10 years, it has be restored MOTed and was running fine, but then started to loose power, back fire and eventually stalls for no reason. To add to the complication of the fault if the ignition is switch off and turned back on the car runs as normal, this started to occur intermittently every 10 minutes but has now got to the point where restarting the car does not remove the fault. I have checked all the normal potential fault points, but can not get to the bottom of the problem, can anybody shead any light on the situation, any help would be great.