Need Help with Engine

[Patrick-Irish]

For months now I've been experiencing this kinda engine hesitation. For a while I suspected a transmission issue but I'm not so sure any more.

This can happen any time, hot or cold engine. It happens on every journey, never gets any better or worse.

For the want of a better word the engine skips a beat. It drops a hundred revs or so, then recovers all inside of one second. It's not particularly noticable when accelerating, it's when you're maintaining a contant speed it becomes most noticable because your steady speed keeps getting interrupted briefly and you notice it. I was a passenger in my own car last week for a long motorway journey and didn't really notice it at all. But as the regular driver I'm fairly in tune with every turn of the engine and I can notice it.

I've changed the spark plugs recently, made no difference. I've also changed one cam position sensor because it was giving an error code. That made no difference either. The main air intake tube from the air flow meter to the engine block has been replaced with a new one, and no difference.

So what else could it be ? I'm looking for ideas guys, anybody have this issue and get it resolved ? Or even give me some potential causes so I can do some troubleshooting ?

Many thanks.