Cavvy 2l 1995 eco engine, warning light on and stalls, loses power?

My 1995 2l cavvy has an eco engine, is stalling, losing power, using petrol++ (20 mpg), also heaters went at the same time. Orange warning light is on most of the time. Rac said it was the air flow mass meter, have fitted a new one without any change, Has been serviced, has a new exhuast system and catalytic convertor. Don't want to keep chucking money at it!!!! Any ideas, mechanic is at a loss?!!!