Rough idle, consumes very much fuel?

The car stood for 6 weeks, started but ran a little rough on idle, only on idle and it consumed maybe double the amount of fuel
Got an engine light, misfire. Then I turned the car in for a timing chain replacement, when I get it it runs terrible on idle, like they slapped on some huge cams. I mean it got that lope now. And it consumes half a tank in less than a week. And the engine light flashes now, but still only on idle, when driving it is lit like normal. Still sounds really good when driving, just consumes alot of fuel. And the engine braking is really jerky, espacially at the lower rpms.
Saab 9-3 aero 2003. Thanks