Did a 150-mile round trip yesterday, mostly motorway. On the way I had an at-points pretty worrying judder on constant throttle; it felt like driving into a strong head wind, or fuel starvation or something. It wasn't there in town driving, or under acceleration. While waiting for a CEL which never came, I was thinking ...
vacuum hoses?
throttle body?
failing DI? [though wouldn't a misfire throw a CEL?]
One diagnostic clue: this seemed to start, on the way, when I engaged cruise. The car was unhappy, so I switched cruise off; but constant m-way speeds still generated the same symptoms. However, on the way back (engine had therefore been re-started), duly wary, I didn't engage cruise - and the car felt completely normal.
Any thoughts?