[Joshboody]

I'm curious as to the fluctuations in idle rpm. this has been happening for awhile now... it's very subtle, hardly noticeable. RPMs will fluctuate from 600 to 700, and sometimes a little higher, but stays fairly smooth. Sometimes you can feel what I consider a slight stutter, like a cylinder didn't fire, but rpm stays smooth.

when watching timing on the gauge it will fluctuate from maybe 0 to 4deg, fluttering back and forth at what seems to be constant rpm. Sometimes no fluctuation.
Why would timing change?

I imagine some of this has to do with the injectors. The car runs smooth and even idles smooth despite above. WOT feels great and datalogs are looking good. less than 10K on new plugs. 60K miles total on car

any thoughts / comments?

[shifterboy45]

is that 0 to 4degrees BTDC or ATDC?

just figuring out if the car is backing the timing off or advancing it--

remember the car is designed to stay in compliance with emission regulations at idle and cruise --

[shiv@vishnu]

Totally normal to see dynamic advance activity at idle. The DME will run between +5 and -5 degrees of advance to comply with emissions regulations and to provide a stable idle. The macro idle control adjustments are made by the throttle blade but all the micro stuff is done by timing control.

[AWD Addict]

Originally Posted by Joshboody

I'm curious as to the fluctuations in idle rpm. this has been happening for awhile now... it's very subtle, hardly noticeable. RPMs will fluctuate from 600 to 700, and sometimes a little higher, but stays fairly smooth. Sometimes you can feel what I consider a slight stutter, like a cylinder didn't fire, but rpm stays smooth.

when watching timing on the gauge it will fluctuate from maybe 0 to 4deg, fluttering back and forth at what seems to be constant rpm. Sometimes no fluctuation.
Why would timing change?

I imagine some of this has to do with the injectors. The car runs smooth and even idles smooth despite above. WOT feels great and datalogs are looking good. less than 10K on new plugs. 60K miles total on car

any thoughts / comments?

I have this same exact condition. I 've had the car in the shop for it multiple times, they've tried everything with no luck.

An I-6 engine should be perfectly balanced, so no stumble/shake should be occurring.

[tscdennab]

My conclusion is that the rough idle saga begins when you install catless downpipes. The ECU struggles to maintain the emissions and since it cannot (rear O2 sensor readings are always showing insufficient emission reduction), it tries all kinds of things that add up to the rough idle.

At least for me, I clearly remember that rough idle begun when I installed catless downpipes.

The only solution would be a flash that correctly disables the emission maintaining algorithms.

[Ilma]

Originally Posted by Joshboody

I'm curious as to the fluctuations in idle rpm. this has been happening for awhile now... it's very subtle, hardly noticeable. RPMs will fluctuate from 600 to 700, and sometimes a little higher, but stays fairly smooth. Sometimes you can feel what I consider a slight stutter, like a cylinder didn't fire, but rpm stays smooth.

I get this too.....idle is smooth, but every once in a while (a couple of times per week sometimes) the car kind of stumbles for a split second at idle and then I notice the DME increases the idle speed from 650 rpm to 750 rpm.

It remains idling smoothly at 750 rpm until I restart the car, at which point it reverts back to 650 rpm as if nothing just happened.

Weird.

[MDORPHN]

Originally Posted by tscdennab

My conclusion is that the rough idle saga begins when you install catless downpipes. The ECU struggles to maintain the emissions and since it cannot (rear O2 sensor readings are always showing insufficient emission reduction), it tries all kinds of things that add up to the rough idle.

At least for me, I clearly remember that rough idle begun when I installed catless downpipes.

The only solution would be a flash that correctly disables the emission maintaining algorithms.

I may be wrong, but I believe that the post-cat O2 sensors are there only to monitor the operation of the cats and have no effect whatsoever on the tune. At least, that's how it is with other BMWs.

Neil

[e90_guy]

I also saw the RPM jumping up and down in the morning. The rpm started out at around 600 rpm and the car felt like it was going to stall but then the rpm jumped up to 1000rpm. After few seconds it returned to around 600 rpm. I have all my 6 injectors replaced last week. Is this normal?

[ren]

Originally Posted by Ilma

I get this too.....idle is smooth, but every once in a while (a couple of times per week sometimes) the car kind of stumbles for a split second at idle and then I notice the DME increases the idle speed from 650 rpm to 750 rpm.

It remains idling smoothly at 750 rpm until I restart the car, at which point it reverts back to 650 rpm as if nothing just happened.

Weird.

We talked about this already on another thread, but I still have the same exact issue. I told my S.A. about it and described this, but the technician couldn't replicate it of course.

I still think it's an issue with one of the coils because I never had this until I replaced my spark plugs. I'm hoping to get a misfire one day so I can replace that coil.

[Joshboody]

advance is best for emissions.
advancing timing with same AFR will increase rpm
so the DME is constantly trying to lean AFR and advance timing for best emissions... a back and forth that causes some fluctuations? Are these adjustments from actual o2 readings, or DME trying to hit best operating conditions for emissions

If i remember correctly from the timing table, idle rpm range with low load is 0 degrees.

Originally Posted by erensf

I still think it's an issue with one of the coils because I never had this until I replaced my spark plugs. I'm hoping to get a misfire one day so I can replace that coil.

I can't imagine a coil being an issue at idle, but NOT WOT, part throttle.

[shifterboy45]

Originally Posted by AWD Addict

I have this same exact condition. I 've had the car in the shop for it multiple times, they've tried everything with no luck.

An I-6 engine should be perfectly balanced, so no stumble/shake should be occurring.

perfect balance has no direct bearing on idle quality -- there are so many factors involved in keeping the engine running and staying within given parameters.

the engine of yesteryear whould idle smooth as glass since the timing was static at idle, and this was the demise of that type of engineering -- it couldnt adapt, and regulations changed.

dont get me wrong, the idle should be smooth, but little flucuation in the idle speed is not abnormal --

other car lines use cushier motor mounts -- somtimes fluid filled to absorb some of this behavior -- so other cars can and do feel "smoother"

now if the engine is misfiring or "hunting" for idle -- that a totally different situation.

[shifterboy45]

Originally Posted by Joshboody

advance is best for emissions.
advancing timing with same AFR will increase rpm
so the DME is constantly trying to lean AFR and advance timing for best emissions... a back and forth that causes some fluctuations? Are these adjustments from actual o2 readings, or DME trying to hit best operating conditions for emissions

If i remember correctly from the timing table, idle rpm range with low load is 0 degrees.


I can't imagine a coil being an issue at idle, but NOT WOT, part throttle.

depending on the nature of the coil failure, it can sometimes manifest itself at idle -- intermittent connections to the coil pack/plug, heat generated increase in resistance --

but your right -- a coil failure is most notably evident under load.

[nuM nuMs]

Originally Posted by shiv@vishnu

Totally normal to see dynamic advance activity at idle. The DME will run between +5 and -5 degrees of advance to comply with emissions regulations and to provide a stable idle. The macro idle control adjustments are made by the throttle blade but all the micro stuff is done by timing control.

And once you install a JB3/4 all that +5 and - 5 degrees advance activity stops entirely.

[Lilbro]

Originally Posted by Ilma

I get this too.....idle is smooth, but every once in a while (a couple of times per week sometimes) the car kind of stumbles for a split second at idle and then I notice the DME increases the idle speed from 650 rpm to 750 rpm.

It remains idling smoothly at 750 rpm until I restart the car, at which point it reverts back to 650 rpm as if nothing just happened.

Weird.

My car recently has been doing this too. Does anyone know what the problems are?

[Renus]

You can try to reset the adaptation of throttle, maybe this help.

[Renus]

Originally Posted by tscdennab

My conclusion is that the rough idle saga begins when you install catless downpipes. The ECU struggles to maintain the emissions and since it cannot (rear O2 sensor readings are always showing insufficient emission reduction), it tries all kinds of things that add up to the rough idle.

At least for me, I clearly remember that rough idle begun when I installed catless downpipes.

The only solution would be a flash that correctly disables the emission maintaining algorithms.

Dude, you are right, my idle rpm problem has been solved by reset the adaptation of throttle, even getting better I have reset the adaptation of gearbox as the technician said that since our cars have been driven for certain of periods, the connecting point between clutch and gear would be worn out a bit, therefore, letting the DME learning the new value is a must.

And he also pointed out my rough idle maybe be caused by my catless downpipe too.