I’m having similar issues on my 35i but mine only manifest at cold start, especially on colder days in he winter. Upon start, the engine will be stumbling for 15 sec and sometimes stall out. Restart the car and runs smooth. For the longest time, no codes. Just recently I got a code for VANOS intake that would clear itself after 10 min. Cleaned both solenoids and switched positions. I had one day where the same VANOS code popped up again but again cleared itself. Strangely enough, the idle is normally fine when the code pops up. Now it’s just back to no codes, but rough idle.

Had a smoke test and no leaks. Plugs and coils are new enough not to be the issue. If it’s not the solenoids, is it the actual VANOS unit? Can a camshaft sensor somehow throw off the VANOS? Trying to think of other potential issues before diving into that expensive repair

Hey guys,

SO I replaced both of the camshaft sensors with new and..... not really an improvement :(

Maybe it drives 10-20% better but still the hesitation and misfiring feeling is there. Not sure where to go now.

I found a thread on another forum and they had a similar issue with their n55. They claim to have resolved the rough idle by filling each cylinder with injector cleaner through the spark plug hole, then extracting (and cranking to expel the remainder) to loosen carbon deposits on the piston heads.

He may be on to something..

I have used chevron fuel system cleaner a couple times in the last 1500 mi or so and there seems to be a slight improvement? It’s that or the warmer weather is helping?... Again, I have new plugs, coils, and injectors, cleaned intake valves. I will say, plugs and injectors did come out with a considerable amount of carbon on them so I can only imagine what the pistons look like.

I was thinking worn valve guides as a culprit (at 186k) but I don’t really have the accompanying noticeably smoky exhaust.

Does yours idle rough? Mine has zero issue idling. It's only under light load acceleration 1500-3000rpms that it feels like its misfiring/hesitating/bucking.

I ran a bottle of chevron techron concentrate through it a few weeks ago but zero change in issues.

My client n52 motor had similar problems cleared up when I changed the oil filter cap which was apparently letting oil past the filter and messing up the oil pressure to the vanos. If your scanner has graphing, plot vanos actual vs requested angle and see if it's keeping up with demand. Vanos sluggish response or disa sluggish response can cause the low rpm moderate load hesitation described.

Yes, especially once warmed up. If I gently creep in drive, letting the brakes drag a bit it can be felt. Slight hesitation *sometimes* at partial throttle.

Oil filter cap is pretty recent. Replaced because the center part would no longer snap in place.

On the note of VANOS- I’ve read other N5X threads where members replaced the little VANOS non-return valves which have a micro screen on the end. I have not checked to see if mine are dirty and I’m not totally convinced it would do much in terms of the idle.

I checked the oil filter housing cap, and it's a little wiggly, but by no means broken/missing. Is this considered OK?

Normal. The critical part is that the tip where the little o-ring lives is intact.

I was getting vanos related errors on customer n52 with wiggly center. They went away after replacing the cap

If the tiny o-ring is intact and the filter snugly fits in the oil filter housing, oil pressure and flow will be where it needs to be. I worked on a 328i that somehow had no center, discovered during an OFHG replacement. No codes but the filter was certainly doing little to nothing just sitting in there