Engine Management Error Codes

Ive got a 2001 V40 SE. Engine Management light started coming on intermittently about 2 years ago, now its permanently on. Volvo dealer pulled some error codes during a service which he listed as ECM-0170 & ECM-0304 and said it would need to come back in for further investigation (umm...sounds pricey!). Fuel economy, emissions and power seem ok, but the idling is a bit lumpy, jumps around 400-800 rev mark often. Dealer reset the codes and the Engine Management light stayed off for about 2 weeks before coming on permanently again, oddly during this time the idling was very smooth, was like having a new car again. Anyone got any pointers ? Happy to get my hands dirty. Cheers

What engine does it have? size, power etc.

Is it a volvo or mitsubishi GDI?

Its a 1.8 Petrol GDI. says Volvo GDI on the engine casing if that helps ?

Hi, I've checked all the info I have, but the diagnostic codes I have listed start with EFI, and don't even have the numbers you mentioned. Do you have any further info? Also, is the car 121bhp or 125?