E46 330i Idle Dip Issue - Am I Being Paranoid

Oxide™

Oxide™

Oxide™

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On the way into work there is a ~1 mile section, known as the mad mile, where if it's empty lends itself to a bit of frisky acceleration - probably the only little stretch in South London I have found that accommodates this. Great as I travel it twice a day :) mostly it's one long traffic jam :(

As I joined the mad mile, I had a little play in 2nd and a bit in 3rd up to 60mph and stopped at the traffic lights at the end.

Whilst waiting for the lights to change, which take aaages, I noticed a very slight shudder and looked at the rev counter and it happened again. Idle revs at around a solid 700rpm but dipped briefly to around 500rpm and then at 700 again.

I drove the rest of the way to work without further hiccups - Is this a known issue anyone can shed some light on? Is the engine about to explode? was my little bit of acceleration at the beginning of the mad mile responsible? Everything was at operating temperature etc.

Also yesterday the oil light came on when I turned the car off so I chucked in a litre of Castrol Edge 0w30 if that is another clue.

I'm hoping it doesn't dip again but want to know if anything impending is about to hit me :eek:
 
I dont know about BMW's but its normal for other cars I have owned but its usually related to when you do something, eg you stop and the car idles normally, you press the brake pedal and the rev counter drops slightly and then moves back to its normal position again, same for use of a window etc
 
Bear in mind I'm no mechanic so a lot of this is over my head lol

I'll try explain it again...

You are sitting at idle, 1 dip occurs, almost like the car is about to stall but catches itself quickly within 200rpm (700rpm to 500rpm and back again - almost unpercievable), 5 seconds later a second dip occurs and then everything is back to normal.

I wasn't touching anything at the time, car in neutral and feet off the pedals

I'm currently reading this thread as I think it's the same thing I experienced
 
[TW]Fox;16942034 said:
Idle control valve.
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This is what I thought, but I have very little mechanical knowledge, let alone BMW knowledge.

Typically the fix is, take it off, spray with brake or carb cleaner, shake and swill it out.

Leave to dry, fit again
 
[TW]Fox;16942238 said:
Yes?
Click to expand...

Odd. So it has a DBW throttle AND an idle control valve? :confused:

DBW usually means the ECU takes over full control of everything, including maintaining the idle. Because the ECU can actuate the throttle whenever and however it likes regardless of the throttle pedal position.
 
PMKeates said:
Maybe, I never fixed it :p
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:D

I think if most people look at their rev counters on their way home tonight they will see that its quite normal in any brand of car. I could be wrong though, it could be something more sinister but you will see what I mean if you are stationary, at idle and press the brake pedal or something
 
PMKeates said:
It is your BMW telling you to stop being a girl and shifting early. 60 MPH is for 2nd only :p
Click to expand...

lol ok it was around 70mph in a 60mph zone. Don't want to push it more as that would be illegal and all ;)

Thanks for all the suggestions guys, reading that thread I linked to it seems it could be a whole manner of things, like vac leaks, ICV, CCV, CPS, O2 sensors, AC? etc.

I'm hoping it doesn't happen again and it's nothing to be concerned about, will have to see how it goes
 
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