Worried

[dreamingat30fps]

So today on my way to work I'm stopped at a red light slight down hill angle. Then I notice the car felt like it was going to die as if I had let off the clutch but recovered. I did not let of the clutch but just to be sure I put it in neutral and waited. It did it again. Drop in RPMs like its going to die and then picks back up. I'm do for inspection 2 in about 6k miles.

Any ideas what could be causing this, getting freaked out it might leave me on the road somewhere.

[partlowr]

Sounds fuel or air related, how much fuel was in your tank? You said you were on a decline so a combination of low fuel level and whatever fuel was in the tank swooshing forward as you braked could have cause a momentary drop in fuel pressure since the fuel pump is located in the tank. A bad MAF sensor can also act this way at low RPM. Is it happening all the time now or just the once incident you explained?

[partlowr]

One other thought, the fuel pump strainer(filter) could be cloged or obstructed as well.

[dreamingat30fps]

That's what I was thinking too, but its not that low on fuel. Maybe like 1/3 tank no low fuel light or anything and the incline was not very steep at all. I faintly recall this happening before but not like 3 times in a row.

[dreamingat30fps]

Originally Posted by partlowr

One other thought, the fuel pump strainer(filter) could be cloged or obstructed as well.

Is this something I can check myself?

[partlowr]

Originally Posted by dreamingat30fps

Is this something I can check myself?

Unfortunately no, the fuel pump and strainer are inside the fuel tank and would require a lift and dropping the fuel tank.

Are you getting any CEL's? these cars are so finicky that if it were something serious a CEL would most likely pop up on your dash. Most fuel pumps pick-ups are located on the bottom center or bottom rear of the fuel tank so they can grab fuel when you are stopped or when you accelerate(fuel swooshes backwards on accel), the combination of the decline and deceleration could have been enough to starve the pump for a split second, however with 1/3 of a tank I would not think this would be the case, the entire pump would be under fuel level even under braking. Go out and fill up the tank and run the same route and see if it returns/continues.

Sorry I could not offer you a more definative answer.

[mshanno1]

Interested to see what you find out, as mine does this too sometimes. I have heard of other people having the same problem

[beta]

A few people commented on a previous thread about this, no solution back then either.

[wss4]

My car does the same. Will usually dip a couple of times every time I drive it, and will actually stall a couple of times a week. RPM dip has become more frequent, and stalling has only started to happen over the last couple of months. Unrelated to fuel level. I am due for inspection II this coming week.

[XMetal]

Mine does this also, but only once or twice thus far. Would definitely like to see what was the cause.

[pyo]

from my previous experience with my E46 3series, it was related to bad VANOS seals. My RPM would idle around 700-800 then out of no where dip down to 200-300. It occurred more when the weather was cold.

[Z4MLover2012]

So at what mileage on the clock is this issue occuring for you guys out there?

[Phishman]

I have had this happen a couple of times and mentioned it when I had inspection 1 done. Of course the dealer couldn't replicate. I have really only noticed it about 10 times in the 2 years I've had the car. Seems like it usually happens after I open it up on the expressway and wait at the light at the end of the offramp. But I would freak if it actually stalled out.

[gcochard]

This has also happened to me, maybe 100-200RPM drop but it doesn't sound like it's gonna die or anything. Maybe happened 5 times in as many months. I will be doing the vanos filter and checking all accessible vanos related things when I am under the valve cover for the adjustment. I will post all that I find.

[dreamingat30fps]

Originally Posted by Phishman

Seems like it usually happens after I open it up on the expressway and wait at the light at the end of the offramp. But I would freak if it actually stalled out.

This is when it happened to me also. Mines at 40k miles and I'm due for inspection in about 6k miles. My friend who has a Z4MC said he had the same issue before he did his inspection also. He said it went away after inspection so it may have something to do with that.

[Shota15]

Had the same problem with my M3 and it was the throttle position sensor, It only happened when I was stopped and the rpm's would drop and I thought the car was going to stall and then it would go back to normal.Iit never showed a code, but my independent BMW repair shop was able to test it with his scanner and found the problem.

[dreamingat30fps]

Scanned for code this is all I got.

5DF4:
DSC-ECU: ECU-internal: ADC calibration error
Error will not cause a warning light
Error is not currently present
Test conditions have been completed

9:
Not an ASC2-message

[gcochard]

ADC...analog to digital converter chip?

[dreamingat30fps]

This is what I found regarding the 5DF4:

5DF4 System voltage LESS than 9 volts.

This code has generated when the battery voltage or supply voltage to the ECU has dropped below 9v (Low Volt code) It was most probably been caused by a flat battery at some point.

I will clear it and see if it comes back. What Shota15 makes sense, not sure if it would throw a code though.

[gcochard]

Makes sense, have you replaced the battery yet or is it the original? I'm on the original battery on my 06.

[dreamingat30fps]

I have not replaced the battery myself and from the service records it doesn't look like the previous owner did either.

[Phishman]

I had my battery replaced and it didn't resolve the problem.