Troubleshooting Stumbling/Stalling at low RPM & Startup

[Mike1261]

I have an 06 E53 with around 105k miles on it now.

This problem has been ongoing since getting the vehicle in August 2018 and putting around 12k miles on it.

It has thus far not affected my ability to use the vehicle normally, but it appears to be getting worse so I'd like to address it and have no idea where to start.

The only codes are for Thermostat Stuck Open and O2 sensors. I have a new thermostat, just no time to install. The O2 sensors and Spark Plugs have all been replaced and didn't really make any difference.

Symptoms:

- When initially starting the car it catches, but takes about 2-5 seconds to stop sounding like the engine is going to die, and then idles normally (albeit it sounds a little low, but I know my Tach reads low due to the needle being re-installed slightly off the mark when doing a speedo KM/H -> MPH conversion, so not sure exactly what the idle speed is). Once it's "ok" it's good for the rest of the time until turned off/restarted.

- When accelerating from a stand still with a low amount of gas pedal it's OK, but if you step on it, say, 2/3 pedal or greater, it bucks a little and scares my wife if we are crossing traffic as she thinks the car will die. It doesn't, but it's not smooth.

- After driving long distance, around 3 hours, then stopping at a convenience store for a snack (engine still running), and then slowly turning out of the gas station parking lot at low rpm and low throttle, the engine will stall entirely. I know it's an odd scenario, but we road trip a lot and I have found this issue to only occur after running the car for many hours. Just puttering around town it's not an issue.

It doesn't appear to be running rough, and under modest acceleration it doesn't appear to have any issues. It seems to be the low speed/low throttle, and engine start-up period that is problematic.

Additionally, this engine has always started up right away, but the past 4 or 5 days it takes 3 or 4 seconds of cranking for it to catch, and the initial "feels like it'll stall" upon startup has gotten more dramatic.

Are these symptoms common? What should I be looking at in terms of diagnosing it?

I have some time today to look at it so I plan to go take a look at the MAF, Throttle Body butterfly plates, see if I can detect any vacuum leaks, etc. But I am on a limited budget so, while I can likely afford to fix the problem, I cannot afford to throw random parts at it :-)

Thanks in advance!

[andrewwynn]

The slow speed parking lot stall (or worse: inch forward waiting for traffic doing a left turn) was the exact symptoms of cam shaft position sensor

With stuck open thermostat you could be running rich in open loop always. Use the hidden menu to determine both the engine coolant temp and also the actual RPM.

[RRATS4]

I have a 4.6is, and it sound like a MAF issue to me.

[Mike1261]

Just got around to changing the Intake Cam Position Sensor.

My preliminary evaluation is that this has fixed the problem. I won't know for sure for a few days of driving it to make sure it wasn't just a fluke that it starts up nicely now, but I'm pretty confident that the problem has been solved!

And I would like to thank andrewwynn for the advice :-D Saved me so much headache and hassle! The Check Engine codes do not indicate any issues with the Cam Position Sensor, as it hadn't completely failed. I think it was just misreading at low speeds and was in the process of failing. It's been acting this way for the 15,000 miles I've owned the car and god knows how long before I bought the car, so it could have carried on without totally failing and triggering a code for god knows how long from now too.

For anyone looking for a Cam Position Sensor, I picked up one on eBay for $33 from the brand "OEM Germany Ab Elektronik"

It is made in Germany and I have found references online indicating that it is the same sensor that OEM BMW sensors are, but without the BMW stamp on them. After closely inspecting it and comparing it to the BMW part I pulled from the vehicle, they are indistinguishable, every detail is identical, and it's not made in China junk from Amazon.

Thought I would update this thread with as much information as I could in case someone else comes along with the same issue ;-)

[andrewwynn]

That's the prob with the cam sensor. They fail-ish. Add long as they sorta work you won't get an error related to the cps, the computer will prefer to believe the cam is going through wormholes to achieve the impossible rates of change rather than believe the cps can send data that gets faster and slower than reality.

It's still a guess and hope it's the correct one. Both our M54 needed new CPS about 130,000 miles. They had the symptoms of turning off the engine for you when you dropped throttle going slowly (like coming to the middle of intersection waiting to turn left or pulling into a parking space).

I bought a similarly advertised OEM part but from Amazon and I felt confident when the directions were in German. Ok paid a lot more, I think I'd maybe get one of those eBay gems just to have a spare. I would never buy a CPS not OE or OEM. (Eg local store)