[DaanBMW]

This has been happening quite often, and I can't seem to find anything reliable as to what could be causing it.

On a hot day, with the a/c on, the car drives ok and idles ok (maybe a small dip when a/c is tuned on). But... when I say come to a full stop at like a stop sign or a traffic light, chances >80% are the engine will die when I take it out of gear in anticipation of the stop or the downshift. The revs just drop like a rock when I shift to neutral in anticipation of the full stop. Unless the a/c is on, it never happens, regardless how hot or cold it is.

All I could find was similar symptoms caused by IDV idle regulating valve / ICV idle control valve but all on older models - however I can't find any such parts on the e9x NA engines.

(As part of the 100k maint I replaced thermostat, water pump, spark plugs, serpentine belt kit, coolant.)

Any ideas ?

[Taskmaster]

Happened to me: clean maf, replace/vanos solenoids and reset adaptations did it for me. When you unplug the maf, see if the car still does it.

[DaanBMW]

Originally Posted by TheAxiom

Happened to me: clean maf, replace/vanos solenoids and reset adaptations did it for me. When you unplug the maf, see if the car still does it.

Thanks. I recall reading your thread but didn't really understand what the root cause really was.

- I'll do the MAF cleanup althought I think that should affect the car in other modes than only with a/c on, or ?
If I unplug it what should happen ? Doesn't it go in limp mode ?

- I had cleaned and swapped the solenoids before, no change. I think I have 2 spares so I'll put those in.

- How did you reset adaptations ? Did you use a BT tool or ? Did you plain reset all or can you select which (read that throttle adaptations resets might cause issues) ?

[Taskmaster]

Originally Posted by DaanBMW

Thanks. I recall reading your thread but didn't really understand what the root cause really was.

- I'll do the MAF cleanup althought I think that should affect the car in other modes than only with a/c on, or ?
If I unplug it what should happen ? Doesn't it go in limp mode ?

- I had cleaned and swapped the solenoids before, no change. I think I have 2 spares so I'll put those in.

- How did you reset adaptations ? Did you use a BT tool or ? Did you plain reset all or can you select which (read that throttle adaptations resets might cause issues) ?

I unplugged the maf, reset adaptations and drove it hard. When I plugged it back in, no more issues..well...the RPMs dip when the A/C is on like it will stall. Do you have a K&N?

[Three_thirty_I]

The N52 does away with the Idle Control Valve and in place of that uses the Valvetronic system for the throttle control (the throttle body is also used differently than other engines). Definitely see what the engine does with the MAF unplugged, but maybe get the codes read before doing this to see if anything comes up.

[DaanBMW]

Originally Posted by TheAxiom

Do you have a K&N?

Nope, stock papaper filter changed every 20k miles. Well I should say Mann filter if that matters but I doubt it.

Originally Posted by Three_thirty_I

The N52 does away with the Idle Control Valve and in place of that uses the Valvetronic system for the throttle control (the throttle body is also used differently than other engines). Definitely see what the engine does with the MAF unplugged, but maybe get the codes read before doing this to see if anything comes up.

Yes, finally a confirmation that there is not such darn valve. I have no codes, at least none active (check OK). Do you mean with a tool that can read stored/non-active codes ?

[DaanBMW]

Tried to replicate today, but weather is a bit colder and seems using the a/c on a non-hot day will not trigger the issue.

hmm... Seems like the adjustments for having the a/c on are working well if ambient is not high. What tells the engine outside temp ? MAF ? Even the rpm dip is almost non-existent on a colder day. The on-board readout is spot-on for ambient temp, always has been.

[Three_thirty_I]

The MAF sensor has two parts to it, it measures the ambient temperature coming into the intake, and then it has a thermistor which measure the air flow based on the ambient temperature. The outside temperature measurement uses an externally mounted sensor completely unrelated to the engine itself.

I would see what diagnostics can pick up, there may be stored faults that you can work with.

[DaanBMW]

Adaptation reset didn't do anything. Logic seems to indicate my temp sensor in the MAF is likely not working right. (...and this might even explain why once I swap to my summer wheels I slowly get a dent in mpg. How the heck does it get better in cold weather ? And no, I'm not comparing w/ a/c vs. w/o, w/ a/c on it's expected.)

Gotta get the MAF cleaner, the one I had for the TDI is empty. Never cleaned my MAF.

Also have to see if I can get some codes read. But shouldn't something so important as the temp being not read raise to the level of a CEL or some other warning ? Or maybe it is being read just completely off/incorrect ?

[DaanBMW]

Did everything except the codes reading, still working on that:

- MAF is cleaned using MAF cleaner spray. Nothing visibly dirty/bad.

- reset adaptations

- on solenoids I actually had 1 spare in v. good shape, so I swapped that for the intake (top) and the best of the 2 I had in I re-used for the exhaust (btm). Both were cleaned using paint thinner, air cleaned and then applied MAF cleaner here as well.

Car drove better this morning, but it did so last time I cleaned the solenoids too. We'll see later today or tmrw - both days should be hot.

[Taskmaster]

I'll keep watching.

[DaanBMW]

Well, turns out the issue is still there on a hot day. When I come close to a stop and shift to neutral the rpms dip abruptly. Sometimes the engines corrects this with a quick surge then holds steady, sometimes it dies.

Given this is my 3rd vanos I used for the the intake, could this be the MAF ? Not reading the ambient temp accurately ? If it doesn't really read ambient temp, then shouldn't that affect the idle speed as well ? Why only w/ a/c on on a hot day ?

[Taskmaster]

Originally Posted by DaanBMW

Well, turns out the issue is still there on a hot day. When I come close to a stop and shift to neutral the rpms dip abruptly. Sometimes the engines corrects this with a quick surge then holds steady, sometimes it dies.

Given this is my 3rd vanos I used for the the intake, could this be the MAF ? Not reading the ambient temp accurately ? If it doesn't really read ambient temp, then shouldn't that affect the idle speed as well ? Why only w/ a/c on on a hot day ?

DId you unplug it and drive around?

[DaanBMW]

Originally Posted by TheAxiom

Did you unplug it and drive around?

Nope, but I'll do that today. What is the expected result - same behavior as the engine doe not know ambient temp ? Or the defaults w/o the MAF readings are compensating the a/c on and the behavior goes away ?

[Taskmaster]

Originally Posted by DaanBMW

Nope, but I'll do that today. What is the expected result - same behavior as the engine doe not know ambient temp ? Or the defaults w/o the MAF readings are compensating the a/c on and the behavior goes away ?

When I did it, the engine would no longer stall.

My issue was -

Would stall when slowing down in gear (usually 3rd or higher) and press the clutch in.
Would not happen with A/C on.

Then when I cleaned the maf, it would do it with the A/C on, but no off.

Unplugged the maf, reset adaptations and drove it hard. Swapped it for another used maf I had around, replaced the vanos solenoids and never had the issue again....

But it still does the rev bounce as if it will stall sometimes. Going to try another MAF.

[DaanBMW]

Originally Posted by TheAxiom

When I did it, the engine would no longer stall.

My issue was -

Would stall when slowing down in gear (usually 3rd or higher) and press the clutch in.
Would not happen with A/C on.

Then when I cleaned the maf, it would do it with the A/C on, but no off.

Unplugged the maf, reset adaptations and drove it hard. Swapped it for another used maf I had around, replaced the vanos solenoids and never had the issue again....

But it still does the rev bounce as if it will stall sometimes. Going to try another MAF.

Sure sounds exactly like what I'm experiencing ! How did you reset adaptation, press start btm w/o turning engine on, then pressing gas pedal 30 sec ?

Why the 'drove it hard' part, what does that do ?

[DaanBMW]

With the MAF disconnected seems this doesn't happen, and even my initial bog down is mostly gone (happens when talking off: the engine revs dip as if ready to die then it finally recovers and car takes off as expected). But to confuse the issue nice enough towards the end of the test w/ MAF disconnected I did get some of the rev bounce w/ the a/c on, but it wasn't as pronounced as it usually is...

[accel]

I had the same issue and brought my (out of warranty) car to the dealer. They identified the issue as related to a recent service campaign (around a year ago I got a letter in the mail on something related to vanos or so), codes suggested that was failed camshaft sensor. Those were shadow codes as I never had CEL come up.

Before they identified that, they said if it's not related to the service campaign, they would try too look and cover that under California emissions warranty.

Mine it manual and sometimes would die not at the stop but at the gear switch in the turn, - pretty scary thing as your power steering is off at that moment.

P.S. Other symptoms I noticed - the car felt underpowered around engine Idle speeds. Like, in tight slow spots, like parking areas I would have to give it some RPMs to move, otherwise the engine would detonate and barely pull.

[yupetc]

If no CELs and you keep having these issues, here's what I would do:

1. Unplug the Eccentric Shaft Sensor and see if it's got oil seepage in the female plug (resides inside the valve cover). If so, you're going to need to replace that POS.

2. Replace both VANOS Solenoids with brand new parts (when i replaced both of these, it did the trick for me, I was having the exact same issue you're describing)

3. Valvetronic motor replacement and re-prog/calibrate.

If your MAF is bad enough, CEL will come up most times.

Hope this would help.

Goodluck.

--
Pete

[DaanBMW]

Originally Posted by accel

I had the same issue and brought my (out of warranty) car to the dealer. They identified the issue as related to a recent service campaign (around a year ago I got a letter in the mail on something related to vanos or so), codes suggested that was failed camshaft sensor. Those were shadow codes as I never had CEL come up.
[snip]
P.S. Other symptoms I noticed - the car felt underpowered around engine Idle speeds. Like, in tight slow spots, like parking areas I would have to give it some RPMs to move, otherwise the engine would detonate and barely pull.

Hmm... mine only does it w/ a/c on. Is that what yours was doing too ? never had issues in slow spots, but the car bogs down when trying to get going from a dead stop.

What did they end up doing, change the camshaft sensor ? I assume on your dime, or ?

Originally Posted by yupetc

If no CELs and you keep having these issues, here's what I would do:

1. Unplug the Eccentric Shaft Sensor and see if it's got oil seepage in the female plug (resides inside the valve cover). If so, you're going to need to replace that POS.

2. Replace both VANOS Solenoids with brand new parts (when i replaced both of these, it did the trick for me, I was having the exact same issue you're describing)

3. Valvetronic motor replacement and re-prog/calibrate.

If your MAF is bad enough, CEL will come up most times.

1. Did check the eccentric shaft sensor, seems dry.

2. VANOS. I know new is always better, but this like the 3rd used solenoid on the intake and 2nd on the outlet. Yet all symptoms are there. Don't get me wrong - I'll buy them in a heartbeat if that is the culprit, but given this history I'm not sure.

3. Valvetronic motor. If that would be the culprit, wouldn't things like my idle be a mess ? Or other symptoms like power loss under load, hesitations ?

------------

Hope to read any codes this week.

[Camman]

This has been happening my car for about a year now. It's quite rare when it happens. Usually once every 4-6 months.

For me it's only happens when the A/C is on. I'm usually coasting in 4th gear and then when I press the clutch in to take it out of gear the RPM's just drop straight to 0. Usually I don't even notice until I see my check engine light come on because the car is off.

The car will usually catch itself when the rpms drop but definitely doesn't feel right.

Once the car stalls and I restart it immediately, the throttle and rpms are acting differently. It's not as quick revving and just feels different when going through the gears. Now I can fix this behavior if I turn the car completely off, taking the key out, putting it back in and restarting. After this, the car is back to its normal behavior.

I'm curious to see what's the true cause of this problem.

[Camman]

Any updates on this?

It happened to me over the weekend.

I didn't even realize the car stalled because after about an hour of driving on the highway and hitting traffic I got into the city and got to a stop light. That's when I noticed the throttle was acting weird. It was acting the same way after the car stalls and I restart it. Well, a short distance later I was making a turn and as I was letting the clutch out to engaged the gear, I noticed the car was off but it was too late and I restarted the engine by engaging the gear lol. So I must have done this while I was in traffic and didn't notice because the car literally restarted from 0rpm so smoothly.