Idling revs

[Phoenix]

Hi All,

Just noticed something i thought a little strange.

Was sat in the drive and thought id just rev the car a little, only to 2k ish, when doing this repeatedly, say 3 times out of 4 it will dip below the idling revs and then reset back up to idling revs after a second. When it dips below if i rev it it seems to struggle to come back above the idle threshold.

Anyone else have this on their car? If others have seen the same issue then i'll not bother mentioning it to the garage.

Cheers!

 

[cj10jeeper]

I think you're just confusing the hell out of it, so the revs drop right down then it settles to its correct idle.

 

[EdButler]

Yeah i agree, its nothing to worry about. If you were doing this while cold, it is most likely the engine running in open loop (cold start mode) and as its warming up, adjusting its fuel/ignition timings.

Either way, no engine will produce 100% repeatable results whether driven normally, on a dyno or wherever else - thats the nature of the beast!

 

[Phoenix]

It does it when warm or cold. If any of you guys could reproduce it my concern would be alleviated.

 

[AlanJ]

Tried this on my 325i and Jeep - they all do it!

 

[cj10jeeper]

I think you'll find pretty much any car with sophisticated electronics will do it.

Alan mentions a Jeep. I know mine does this as it has specific anti stall software that when you go on an off the throttle quickly it prevents stalling and in so doing splutters around, then over revs slightly above idle, then settles back.

Try raising the revs slowly then lowering them just as you would while driving and see what happens

 

[Andy]

I was going to moan about this too, but not from your experiment, it would do it frequently when say, in traffic, coasting to a halt and taking it out of gear with the clutch in - almost sounds it's going to stall.

i think ed's hit on it closest recently, this seemed to happen a *lot* more in mine when i was using cheapo fuel.

 

[Phoenix]

YEah ive noticed the sound like its going to stall when in "stop start" traffic.

Also when pulling away from a "T Junction" up a hill... when you have to monentarily hold it on the clutch it can appear like its gonna stall before the revs build.

At least we all have these issues and its not a fault as such.

On a positive note i put a little too much throttle on when pulling away at the petrol station and when i took my foot off the gas there wa s amassive bang at the forecourt. Made some customers flinch... cool.

I have used bp 97 and am currently using tesco 99.... is it better with v power?

 

[Andy]

Excellent thread about fuel by Ed in the general forum, Shell are now doing 99 too so that and Tesco99 are the best.

I used bp97 the other day and was a little disapointed, not least as it's the most expensive of the 3.

 

[Phoenix]

Well it was sainsbury's 97 ron which apparently was/is bp ultimate.... dont know how true that is.

Either way im on tesco 99 now!

 

[JazzFM28]

I've notice mine doing this, mainly when coming to a stop and you knock it out of gear, the revs drop below normal idling level, then the engine blips automatically, and then the revs settle at normal idle.

Its less noticable when sport buttom is pressed.

Also, I notice a horible flat spot in throttle map in normal (non sport mode), at about 1700 - 1800 rpm, when the engine seems way 'off cam' (to coin an old phase, and just like driving an old cross flow with a big can in it), then at about 2000 rpm the engine pulls smoothly. Its less noticiable in sport mode, and not too concerning, but wondered if its worth having it looked at, as its still in warranty.

On a side note, can you get the map blown over with a new one. Dont need more power, but a better map might help drivability.

 

[thattallchap]

Andy, does tesco99 make a real difference?

Whenever i've used premium fuels I've never really noticed a change in any Beemer i've owned (that said i've always use SuperUL 97 on the Z4MC), however my Alfa's loved the stuff - the GTV V6 Cup went like a damm rocket on Opitmax!