575 uneven idle

2003 575 with 24k miles, the car has developed a very uneven idle, feels like it's running on 10, maybe 11 cylinders. Misfire is evident up to 2k rpm but difficult to know if it's still present above this, engine seems to rev OK and car goes plenty fast enough. At random times I get a yellow EML which will clear on a battery reset.

I've doen numerous battery resets with 10 minute reset of values, today it was reset on an SD2, only error showing was a temporary knock sensor.

Tonight I spent a while poking and prodding, there is no obvious big air leak, All vacuum hoses appear sound, I've checked all coil connections and even removed them one at a time to see if I can identify a bad plug/ coil but it's near impossible as the engine note/ idle doesn't seem to change even when you pull three at once!

Any and all advice gratefully received

thanks

 

Just an update if anybody is searching and finds this thread fault has been traced to failed inlet manifold gaskets, once pointed out it's visible that the gaskets have been pushed out from between the head/ plenum tracts