[AllHailKingVolvo]

Hi all,
I've noticed recently that my 940 tends to lose a bit of power when warm, or ten mins into a journey, and gets a bit hesitatey (for want of a better word!) up hills and under power, as it did before I did an ignition system overhaul.

Yesterday, I fuelled up and noticed that there was a significant vacuum buildup in the tank when I took the cap off...more than I have experienced with other cars, and not something any of my previous Redblocks have done.

Oddly enough, the car ran like a peach for the next ten mins, then the running issue reoccurred. On my return journey, the same thing happened...ten mins of smooth, then the lumpiness was back.

So, I pulled over, unscrewed the fuel cap by 2.5 turns and there was the vacuum again. Immediately the idle smoothed out, I hopped back in and took off, and the car was instantly much better. LOADS more power and a lot smoother.

Any idea what is causing this? A duff cap or a blocked evap system?