Heater Problem, Engine Management Light

[cali]

A week ago I started to get a curry like smell from my heater when blowing out hot. This smell over the course of the week turned to a burning like smell. I got a sparky to come check out the motor and other electrical that deal with the heater but to no joy that everything was running fine. Also in that week I took it to a garage where they also checked for the same thing and found nothing but then looked for holes leading from the engine into the car (not sure exactly what they did) and they found nothing wrong there. Now today the smell is getting worse and also the engine management light came on and the car is sluggish and wont accelerate past 50 most of the time unless am going downhill. Any ideas would be appreciated. Citroen xsara, 52 plate 2.0 HDi