Timing issues

Here's the gist:

I was driving down the road with cruise control on and all of a sudden when I went to accelerate past a couple cars, I felt a rough rumble that shook the car and diminished acceleration/horsepower. Since then, It happens every once in a while and I haven't been able to pinpoint any cause to trigger it.

Now, I believe it is a timing issue because when I turn the car off and then pop the clutch or re-start it at a stop, it fixes itself.

Is it, a timing chain tension-er, the chain itself, the cpu, something else? I am going into BMW this week and would like to point them towards the issue.

Thanks for any help!

What does it sound like when it happens?

VANOS is leaking or solenoid is malfunctioning?

I haven't heard anything different. If any sound it is a shudder from vibration. The vibration feels like something isn't balanced, so at first I thought it was a drivetrain issue. After restarting the car and everything was fine I began to think engine which would answer why I lose horsepower and why simply restarting fixed the symptoms.

I haven't seen any leaking and I have been monitoring it pretty closely since this began.

Again, I appreciate the help and any more suggestions are more than welcome.

spark plugs that are going bad tend to give a shudder on acceleration. I'd start with issues with spark if the car trembles and bogs down when you press the gas harder.

I would start with spark plugs. Last time you changed em? Replace coil boots or ignition coils. If you have no CEL could be your DISA valve is on its last leg just could be the start of it going. I would say check the DISA valve first its a very easy check just two bolts and a harness. You could eliminate a lotta guess work with that simple check. The DISA valve from my experience and other posts here have been attributed to the DISA. Especially at cruising speed thats normally when the DISA valve is active.