[granadablanca]

Hi all,

Just curious about an idle issue. Car is a 330i, AT. 69K miles.

My idle had been getting pretty unstable lately (anywhere from 500 to 900, constantly changing every few seconds, like it can't figure out where it should be). Sometimes it'd also get stuck up at 750-800 for no reason, and remain that way for the rest of the drive.

I also had occasional light shaking, usually just on startup, but that seems common enough. Every now and then, though, I'll get a HUGE shudder or two, where it almost feels like an earthquake, but this is rare and has never thrown an engine light. I don't notice anything happening with the needle when that happens. Dunno what the deal is with that.

Anyway, I recently had all adaptations cleared, new DME software installed, VANOS solenoid cleaned, etc. That seemed to help a lot, and now it sits smoothly right at 600...mostly. Was perfect at first, and now seems to be going back to the way it was. Here's what I'm still noticing:

1. When braking to a stop, the idle will still dip down too low, to 500-550, before recovering. Perhaps more so on hard stops, but can't be certain. In every loaner I've had, this doesn't happen. Never drops below idle.

2. It'll still often take a few "tries" before settling at 600. For example, after the dip described in #1, it'll go to 700 for a few seconds, then 650 for a few seconds, then finally settle at 600.

3. It still held a high idle (750-800) until shut off. This has only happened once since.

4. Still some light shaking at startup. Occasionally when warm too. Tough to say if the needle is fluctuating or not. May be unrelated to idle.

Anyone have the same issues? Any thoughts or opinions on this? Normal? Scary? Anything I should do? The car feels fine, I'll only notice this when looking at the needle.

For what it's worth, I only ever get gas at Chevron, but haven't done an actual bottle of it.

Thanks!

(PS - these rpm numbers are eyeball guesses, obviously. I don't even have the hundred-marker on my tachometer, only 500 increments.)

[e90pilot]

I've been having the same issues. It could be a dirty fuel system, old spark plugs, broken PCV system, or other bad sensor. The first three I mentioned might not throw a code at all. The PCV lines are known to get brittle and crack. That would definitely cause idle issues. I know I have broken PCV line and I believe that is the culprit of my issues.

[benzo23]

Mine does the same from time to time too pulling up to a stop light...The idle will drop and make the car shutter and ill immediately look at the tach like wtf...

[fdriller9]

It sounds like when you guys come to a stop and the idle goes down, it's the NIC (Neutral Idle Control) disengaging the diffs. When you drive off, it will reengage the diffs.

The dip is most likely a result of the load being taken off the engine.

This is also the cause of the sticky brake issue.

[inline607]

Yes it is the idle control. Our cars don't have the conventional throttle butterfly valves in the intake manifold. They are all electronic/solenoids. Yet there is a throttle sensor for the idle. Your
ECU might be throwing codes by now. Have it scanned for codes.

[granadablanca]

I've had the NIC disabled for quite a while now. Couldn't stand it. Same with soft-stop. Believe me, I'm well aware of what it is, and this isn't the same.

So, that's not the case here, at least for me.

Any other ideas?

[granadablanca]

Originally Posted by inline607

Yes it is the idle control. Our cars don't have the conventional throttle butterfly valves in the intake manifold. They are all electronic/solenoids. Yet there is a throttle sensor for the idle. Your
ECU might be throwing codes by now. Have it scanned for codes.

Not the idle control, and no codes - I scanned it about two weeks ago.

[granadablanca]

Originally Posted by *********

It sounds like when you guys come to a stop and the idle goes down, it's the NIC (Neutral Idle Control) disengaging the diffs. When you drive off, it will reengage the diffs.

The dip is most likely a result of the load being taken off the engine.

This is also the cause of the sticky brake issue.

To clarify, the rpm dips below idle for 3-4 seconds, max, before recovering to normal. Happens right before coming to a complete stop (say, <5mph), and takes another few seconds before "noticing" and then bouncing back up. Meaning, it doesn't wait until I'm stopped before dipping - it almost feels like the brakes are somehow "dragging" it down. It never lasts longer than a few seconds, and doesn't wait until I begin moving again to return to normal. It's also a fairly new behavior.

Also, NIC isn't necessarily the cause of the sticky brake issue, unless you also get a distinct "bump" about two seconds after stopping (feels like someone rear-ending you gently). If it just feels like a hesitance to release, almost like there's gum under the brake pedal, it's more likely the start-off assistant, which can't be disabled. I've been up and down the NIC/Start-Assist road for years. Both are stupid features, either way.

[e90pilot]

I still say broken PCV line.

[fdriller9]

Originally Posted by granadablanca

I've had the NIC disabled for quite a while now. Couldn't stand it. Same with soft-stop. Believe me, I'm well aware of what it is, and this isn't the same.

So, that's not the case here, at least for me.

Any other ideas?

Didn't you say you had a new DME programmed? Did they disable NIC again?

I bet they didn't...

The only other thing that I would suggest, that no one has mentioned yet, is to clean your MAF.

[fdriller9]

Originally Posted by granadablanca

To clarify, the rpm dips below idle for 3-4 seconds, max, before recovering to normal. Happens right before coming to a complete stop (say, <5mph), and takes another few seconds before "noticing" and then bouncing back up. Meaning, it doesn't wait until I'm stopped before dipping - it almost feels like the brakes are somehow "dragging" it down. It never lasts longer than a few seconds, and doesn't wait until I begin moving again to return to normal. It's also a fairly new behavior.

Also, NIC isn't necessarily the cause of the sticky brake issue, unless you also get a distinct "bump" about two seconds after stopping (feels like someone rear-ending you gently). If it just feels like a hesitance to release, almost like there's gum under the brake pedal, it's more likely the start-off assistant, which can't be disabled. I've been up and down the NIC/Start-Assist road for years. Both are stupid features, either way.

Well I think in theory they are great ideas. However BMW did not implement them very well. They don't function smoothly.

I still think it's NIC. I mentioned above they might not have disabled the NIC feature after reprogramming your DME. Software changes have been made to modify the NIC feature (for the better), it still sucks though. I had my car updated because I had an alarm coded in and while it was being programmed, BMW NA decided to do a nation wide update to all the service stations. So the programming got interrupted and corrupted the software on my car. They had to update to the newest software to reinstall the alarm coding.

[Ph0zenstone]

its most likely a vacuum leak. I had the same issue a while back and finally the dealer found the problem and replaced the vacuum hose going into the airbox

[granadablanca]

Originally Posted by *********

Didn't you say you had a new DME programmed? Did they disable NIC again?

I bet they didn't...

The only other thing that I would suggest, that no one has mentioned yet, is to clean your MAF.

Ha, you're good. I made sure NIC was still disabled after the updates though. Besides, it was happening before the DME update anyway.

Cleaning MAF a DIY? Was a piece of cake on my old Hondas, but these things are like space ships to me. if easy though, it's certainly worth a shot.

[fdriller9]

Originally Posted by granadablanca

Ha, you're good. I made sure NIC was still disabled after the updates though. Besides, it was happening before the DME update anyway.

Cleaning MAF a DIY? Was a piece of cake on my old Hondas, but these things are like space ships to me. if easy though, it's certainly worth a shot.

Not too much to it. There are 2 torx screws securing the MAF sensor to the intake tubing.

I beleive they are T15 torx screws. Remove those and wiggle out the sensor. It's a pretty tight fit so be careful. Get MAF cleaner and spray it 15-20 times, short bursts.

Make sure it COMPLETELY dry before re-installing.

[ska///235i]

I also get the RPM dipping when coming to a stop, but it only happens maybe once or twice a day. It’s hard to describe it, when car is almost to a complete stop, rpm will lower by just a tiny bit and it jumps right back to normal idle for no more than 2 seconds. It's a very small RPM change, but it can be enough of a variation to notice. It almost feels like someone bump your rear-end as someone mentioned above.

This started few months ago and doesn’t appear every day. Car has 44000 miles (06 325xi) with performance intake + charcoal delete, performance exhaust, & PBX. I’m blaming this on the PBX…lol I’m not sure why.

Could this be caused by the power brakes work off engine vacuum and causing a slight difference in engine RPM due to the small temporary vacuum drop in the engine when you hit the brakes?