Hey all been doing some digging into this but keep coming up with a lot of random stuff.

I have a 08 535xi with 89k miles on it, auto Trans bone stock. When driving around 60 mph in 6th gear, on cruise control it feels like the car is stumbling. It loses power for half a second then gains it back. It happens pretty repeatedly. Here's what I have found so far.
Possible fouled plug or coil pack bad, I checked mil with my scan and have no faults.
Carbon build up. I haven't done it since I have owned it. Don't have previous owners history.
Hpfp and injectors. Whole fuel system was overhauled 2 years ago. All 6 injectors and new hpfp.

Any other suggestions? I'm gonna order spark plugs just in case because they are due to be changed but I'm at a loss for any other causes.

Thanks!

 

Are you checking with a generic OBD tool or a BMW specific tool? The BMW specific ones show more detail and probably faults the others don't.

 

Just a basic scan tool. My BT dongle for carly isn't working. I know there's a second set of codes but I was under the assumption a knock would register a cel not just a secondary code. Correct me if I'm wrong tho.

 

Don't know which shows up on generic and what on BMW specific.

 

Mine stumbles periodically but has never thrown a CEL. Even when it went into limp due to misfire and needed to be restarted. After restarting it was fine and has been for nearly a year. Time for new plugs, and maybe coils on mine. 170,000km

 

Preventive maintenance. You should address the first two comments you made regardless of
code checking. Plugs on the 535xi should be replaced every 45k. So you should be going into
your third set. If you don't WOT the car fairly regularly you are asking for carbon build up on this
model.

 

OK got the new spark plugs in... found oil in the nr 3 spark plug and around the coil. I'm guessing when my old lady topped it off she spilt some. Also noticed plugs were very burnt. I bought the car at 68k so these might have been the original plugs... I missed the whole 45k part I thought they were good to 100....

So far haven't noticed the stumble come back.

Also I gotta get the rental for the carbon blasting cause I don't want to pay a few hundred for a cleaning I can do my self. I do drive the car pretty hard but I'll have to take it apart and see.

Thanks for your help!