Low idle and engine vibration when warm and more

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DaniTD
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Post Thu Mar 14, 2013 11:33 pm

Despite changing some parts on the engine, I'm out of luck with this M40.
I put new ICV, TPS (adjusted correctly), AFM, plugs, etc. Changed one bent ignition wire, all of the are now ok. All electrical stuff seems to be right. No vacuum leaks found. Fuel pump new, FPR running right.

So this is the case:

-when starting at cold, engine revs to about 950rpm (high idle, maybe it should be a little bit higher). No vibrations from the engine could be traced.

-when the engine is fully warmed up, it starts to shake, idling at about 700rpm (they should be 800+-50). It only seems to do this when idling. You can see the engine vibrating very fast with hood open. If you put the foot on the gas vibration dissapears.

-if when warm, I turn it off and then, 5 minutes later, I start it again, it goes down idling at 650rpm aprox and vibrating more. After some time idling (30-60 seconds aprox) or if I start driving it, idle returns to 700rpm.

-if when warm , I turn it off and then, 50min later (temp gauge showing a bit off the blue zone, so its not cold but not fully warmed up either) I start it again, idle goes to 750, bounces to 650 softly, then again to 750, again to 650 and finally stabilizes at 700.

Could it be a lean running condition? So when it's cold mixture is right (and it should be a bit overfuelled), when warming up a little lean and therefore idle bounces some times before stabilizing, and when fully warm its too lean that cause a rough running? It's the only thing I can think of, but don't know why :cry:
soul4t
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Post Tue Mar 19, 2013 9:41 pm

Hello mate,

I'm still having hesitation issues on mine and the same hot running symptoms that you have...I'm thinking the next step is to replace the intake gaskets again, but maybe get obsesive with cleaning of the mating surfaces...I have heard that even though air leaks are undetectable, doing this can solve it!
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Brianmoooore
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Post Tue Mar 19, 2013 9:46 pm

A weak mixture will make an engine without idle stabilisation hunt at idle.
Have you had the injectors on this engine rebuilt in the last 50,000 miles?
soul4t
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Post Tue Mar 19, 2013 9:54 pm

Hi Brianmoooore!

Don't our M40's have idle stabilisation?
FYI my injectors were done about 8000 miles ago...slight improvement...as with richening up on CO pot (I know as I'm sure you know by now!) so does point to lean condition in my case...anyway...sorry to thread hijack!
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Brianmoooore
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Post Tue Mar 19, 2013 10:17 pm

Yes, M40s have idle stabilisation, but the feedback loop has an inherent time delay, so it's not perfect. It's designed to deal with relatively long term changes in engine load.
soul4t
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Post Tue Mar 19, 2013 10:33 pm

Ah I see!

Thank you for your insights!
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Billwill
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Post Wed Mar 20, 2013 7:26 am

Have you tested the Blue Sensor?

Does the number 4 ignition lead have the sensor wrapped around it?

I find NGK plugs are the only ones to use.

Is the ICV valve fitted the right way around?

Did you replace the AFM with correct part number....what year/model is your M40? :?
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DaniTD
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Post Wed Mar 20, 2013 2:57 pm

Billwill wrote:Have you tested the Blue Sensor?

Does the number 4 ignition lead have the sensor wrapped around it?

I find NGK plugs are the only ones to use.

Is the ICV valve fitted the right way around?

Did you replace the AFM with correct part number....what year/model is your M40? :?
The sensor around the 4th ignition lead is broken, I have a spare one but people here told me it doesn't have effect on running condition (I read on BMW manuals that it is to make the injection work semi-sequential instead)

The blue temp sensor was tested and working properly :?

New NGK plugs as recommended by BMW (BMW High Power Spark Plugs, aka NGK BKR6EQUP) if I remember correctly.

ICV is new and fitted with the arrow pointing to the intake.

Injectors... don't know if they ever had been refurbished. Engine has 252000km. I checked for intake leaks and didn't found anything new, the only ones I didn't change were the o-ring between the throttle and the heating plate and the intake-to-block gaskets.

The AFM is the same reference as the one I took out... year 1990, non-cat :cool:
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Brianmoooore
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Post Wed Mar 20, 2013 11:00 pm

DaniTD wrote: Injectors... don't know if they ever had been refurbished. Engine has 252000km.
If not, which is probable, then I think they might be due!!
There's no feedback loop on these engines to trim the mixture, so injector performance is of paramount importance.
broadie
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Post Thu Mar 21, 2013 11:27 am

Has the throttle body been cleaned latley?
Ive been told carb cleaner and a tooth brush.