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Discussion Starter #1
Hi all,

I own a black 159 2.0 JTDM TI full options from 2009 since 2014 with 200.XXX on the clock and it's running stable since then. It is an absolute tank and has never let me down since ownership. Loving every minute walking to it and driving in it. It only needs its annual maintenance at a specialist and after that, the fun and games can begin again :).

Since last year especially during the winter season, I noticed that the idle mode of the engine sometimes flicks the needle to 1000 RPM while it should float somewhere at 750 RPM when in idle mode. This is what happens:
  • I start the car and let it run idle. The needle stays nicely at 750 RPM for 10 seconds.
  • After 10 seconds, the needle slowly progresses to 800 RPM, 900 RPM until it reaches 1000 RPM and stays there for 10 minutes. You can clearly hear the engine making more noise as you expect when revving it more.
  • After 10 minutes, the needle slowely returns back to the 'normal' idle range of 750 RPM.
During this whole phenomenon, no regeneration is happening which causes a high RPM for a short period of time to clean out the DPF. I once told my specialist this phenomenon but he couldn't find any fault or error codes or anything causing the above. The phenomenon doesnt have a negative impact on the car besides it making a high revving noise when reaching 1000 RPM.

My question: what determines how high the RPM value should be of the engine in idle mode? Are there any sensors which might need some attention/cleaning? I can imagine that a couple of parameters are measured (pressure, air coming in etc?) before the car/CPU decides to rev the enigine more or to let it sit at the default 750 RPM when idle?

Thanks in advance,

AlfaliNL
 

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Discussion Starter #3
Great tip. Can I do this cleaning myself or do I need a mechanic to do it? Where can I locate the LMM and MAP in the engine bay? Is the cleaner really called LMM cleaner?
 

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As diesel principle means always running on a surplus of air, the number of revolutions it's putting out all depends on the injected fuel (duration/pressure).

So, basically it is ECU controlled by input from accelerator pedal position (fly-by-wire) and (what I presume) parameters such as outside temperature (right-side mirror) and/or cold air intake temperature (MAF, right above the air filter casing), inlet air temperature (iMAP, at the back of the manifold), coolant temperature and lambda value (running rich or lean).
On top of that protected by a temperature sensor sitting sideways behind DPF onto the exhaust manifold (turbo input temp). There must be one other temperature kind of sensor (I think, could be mistaken here) somewhere mounted, that is used to squeeze injected fuel amount and therefore power. Avoid running too hot and ruining things. I know this because from a previous remapping of my ECU, causing a diesel knock, this was flagging necessity to tweak it. Not by MIL on the dash, but by a small hick-up going through the full rev band width.

Those are some of the parameters I'd try to check first. Lambda sensor can also be cleaned - carefully (anti-seize grease ruins the sonde). Yet, this sensor commonly throws up a code at 2.0 versions, causing it to run into limp mode. See below own experience.

I've the same engine from MY2009, built 2010-05. Owner since 2014 (from 70k KM) and still loving it - just as much as you do. (I developed this odd habit always needing to turn my head when walking away from it. It took me time to get used to driving diesel after the revvy twinspark, boxer and GTV6. It simply cannot be compared to petrol characteristic at all - it's another manner of driving relaxed long-runs, yet quick and agile through traffic when necessary - instant pull. To me there's no comparison, both have their own pros and cons.)

So far at 160k KM now, I only had issues with aforesaid lambda (DTC P0130 and P1131, first cleaned it, but eventually replaced it at 105k KM) and a dodgy turbo input temperature sensor (DTC P242A, P242B, replaced it at 85k KM after a few times having to drive it worse than Ms Daisy does back home without boost).

Normally it idles rock steady at 700 rpm. Whenever it's cold outside, during what winters used to be, it sometimes runs higher on idle during warm-up fase. That can take up to approx. 10 kilometers. Noticeable at each red light in between, on my daily commute that is about your 10 minutes. But it is never quite as high as more than a 1,000 rpm, more like 800-900 perhaps. Not as high yours tends to do?
 

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... just realized that a faulty EGR behavior can also influence rpm . Yet, as I wrote earlier, the behavior you described sounds quite normal.
 

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Discussion Starter #8
Thanks Leo for your input. I must say the rough idle-ing only is happening since last year while I have the car for 5 years now. It never behaved like this in the beginning so I don't know if this is 'quite normal'. Cleaning the MAF sensor might be a good one as I assume such tasks are never done during annual maintenance as prescribed by Alfa Romeo.
 

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Discussion Starter #10
Ah interesting. My 159 was tuned to 200 BHP and the EGR was mapped out/closed. Is cleaning EGR then still applicable for me to cure the phenomenom of rough idle-ing?
 
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