I have a 2000 s40 with 116k. The engine seems to run rough between 1000 and 2000 rpms?? Have a p0420 code, changed both cats and 02 sensors with no help. I rev the engine up and let off it's smooth until the 2000 rpm range and i feel a shutter. Happens when driving or idleing. Any suggestions??

 

What plugs? coils cracked? is all the basic igniton stuff Volvo and in good condition?

 

I agree, is the throttle body dirty? How long ago was this replaced? What about the IAC