Camshaft position sensor failure symptoms

[Twistytee]

I searched some similar threads on the topic but my situation seems to be a little different (M54B25 manual). I’ve had a periodic issue with oscillating idle at stoplights where the rpm’s begin rising up to 1200 and falling below 600 several times until the engine stalls. I’ve been able to manage it by blipping the throttle while stopped and moving into traffic. Last week the engine completely stalled when pushing in the clutch and turning through an intersection. No codes whenever I check the car. No rough running at speed and no difficulties starting the car. This only happens at intersections while at idle and is intermittent. Car has 108k on it.

In the last year I’ve replaced the CCV, replaced the ICV, replaced the upstream O2 sensors, rebuilt the DISA, and checked the plugs. Vanos seals are still original. I’ve checked all the typical vacuum leaks and can’t find any. I’ve also cleaned the MAF multiple times. I’m starting to think it’s CPS related, but don’t want to throw parts at it. Any ideas?

[capebmw]

I have seen posts or videos on how to test the Cam/crank sensors. Look for those. Pretty simple process if I can remember. And, after all the other work/parts you have done to the car a CPS really isn't that expensive.

[sienayr]

Can you reset the throttle body on the I6 by turning the key on for 30 seconds, like with the V8s? If so something easy to try.

[JimLev]

Sounds like it could be a combination of the vanos seals and cam sensor.
I’d do the vanos seals, just to be able to rule them out. At 108K they can’t still be good.

[Twistytee]

I was planning to do the vanos seals this summer. It’s not a particularly hard job on the I6 cars, just time consuming and tedious. The e39 is my daily so I have to put it out of commission over a weekend to knock out this job and a few others on the list. I can remove the vanos solenoid and pull the camshaft position sensor to test it with a multimeter but I’m guessing it will test fine since it’s not occurring regularly enough to throw codes. Old posts similar to this seem all over the map with anything from vacuum leaks to sensors to fuel pump/filter regulators, etc. listed as potential culprits. Would leaking vanos seals cause exhaust cam retarding? Does that sensor fail as frequently as the intake CPS?

[TiagE39]

Usually when the cam sensors go on these cars they fail completely, but they can lose sensitivity with age. That said, this sounds more like VANOS seals.

Have you tried resetting the DME and throttle adaptations? Any trouble codes?

[Twistytee]

I had the throttle body off when I did the OFG, OPG, and rebuilt the DISA. After cleaning the TB and installing new gaskets, I reset the adaptions. I have no SES/CEL and no stored codes using my Peake reader. My INPA laptop died so I need to load a copy onto a replacement in order to read fuel trims or MAF settings. Could be Vanos although I’ve read posts on the e46 forums that said replacing the seals didn’t rectify this type of rpm surging/stalling. And the Beisan site seems to imply low rpm hesitation/stalling is more of a vanos seal issue for M52 than M54 motors.