1.8i Petrol, but sounds like a Diesel

I'll move this to the s40 technical forum where it will get more replies.

I have had similar simptoms and it is 2 separate issues. The rattle is possibly the hydraulics tappets. These need oil pressure to make them run correctly and the tend to get covered in laquer from the oil if it is not kept very clean. There is a product that will help fix this available from Halfords. The erratic idel is due to the fly-by-wire throttle body getting coked up. It can be cleaned out during service easily enough and should sort things. If it doesn't then it might need a trip to Mitsubishi for a shot blast with wallnut shells through the inlet manifold. This takes a couple of days to do but is not a costly as it sounds! Jeff

The B4184S2 is the Volvo 1.8 engine so it's not the GDI. I suspect the noise you are having is from the VVT. Quite possibly the tappets are playing up as well. On the top of the engine is the VVT solenoid, If you remove the engine cover and unplug the VVT Solenoid does it make a difference at all? Guide here if you need it: The 2nd issue is odd, Sounds like the idles are getting too slow to keep the engine running. As your revs are fluctuating then that could be the reason. Check the throttle cable for any slack as well as the throttle body/flap to ensure that it's not causing you any problems.