MQ GLX random high idle

[Pelister]

Hi,

Have a GLX Mq that has been having issues with random high idle. Normal idle is 600rpm, but every now and then for about a day or so it will idle at 900rpm. This causes the fuel consumption readout to go up to about 12L/100km or so, whereas I usually get 7.5-9L. This will usually last for about a day and will resolve itself and return to a normal idle the next day. Sometimes it resolves itself much quicker. All of this is without air-con on. The engine idles at 900rpm with air-con on and does not affect fuel consumption readout. The strange thing is, when it is having the high idle problem and I turn the air-con, it doesn’t raise the idle further, it stays on 900rpm.

This has been happening since I bought the car new in Feb. I got them to look at it at the 1000km service. They said they reset the computer which should fix it. But no luck. First 15k service will come up in Jan and I’ll tell get them to look at it again.

Anyone had any similar experiences or any ideas on what may be causing it ?

Cheers,
Peter

[RHKTriton]

Could this be a SQL trim sequence kicking in?

Other possibility maybe intermittent problem with one of the sensors.

Garbage in garbage out applies to all programmable devices, inc ECUs.

[explorer.dave]

Can't talk for the MQ but with the MN's this happens on occasions, as RHK said, SQL (small quantity learn) on the fuel injection. If it is like every 2nd day then look for another reason.

[shawty950]

dpf burn?

[Pelister]

It only really happens at the most every couple of weeks. Is it anything to worry about?

Now that I think about it, after it happened yesterday it did have a burnt smell when I got out of the car.

What is dpf burn?

[aquagen]

Diesel particulate filter re gen aka dpf burn. Increases fuel to engine for a short period to increase exhaust Temps in dpf and clean out the accumulated crap.
It's supposed to be unnoticeable though. And not something you want to stuff up as replacements are very expensive

[Pelister]

Thanks aquagen. So you are saying this could be a normal engine maintenance type of thing? How often would you expect it to happen?

It's definitely noticeable, you get the surging in low gear when the car would usually just crawl along.

[explorer.dave]

It's definitely noticeable, you get the surging in low gear when the car would usually just crawl along.

I wouldn't have thought that you would experience surging even if the dpf is doing a burn, higher engine rev's at idle yes, but surging may indicate another problem.

[Pelister]

The surging is nothing crazy, but enough to notice.

[aquagen]

Shouldn't have any surging. Iv had mq for over a year and never noticed it. If you do lots of short trips the dpf can block and will have a light on the dash. Will eventually lead to limp mode and dpf failure.
I'd be getting it checked by Mitsubishi

[explorer.dave]

I would be taking aquagen's advice, I don't have an MQ so can't really offer much but that doesn't sound like normal SQL or DPF burn, take it to the dealer, that's what your warranty is for.

[MakoShark2]

MN with DPF (euro model) with 58.000km and not a single time I've noticed the DPF burn, although it's happening.

About that, I was told by the dealer that for the recycle procedure of the DPF to engage, engine needs to be real hot.

Optimal conditions would be after 30mn of driving above 100km/h. That's why a frequent short trips use will prevent the process and consequently block th DPF.
After that you'll get the light on the dash, and the dealer will have to trigger manually the process to burn the crap out of the filter.

The cleaning is achieved by injecting a bit of diesel into the DPF which will ignite (hence the need to have the engine hot) and burn the particles inside the filter... Almost perfect, if it wasn't the fact that in the process part of the diesel can spill inside the crankcase mixing with the engine oil.

That's why maintenance intervals are narrower for DPF equipped Tritons (here 15.000km vs 20.000km for non DPF) and you have three marks in the dipstick (min, max, X)

http://www.mitshelp.com/micont-1028.html

So to have a DPF burn you need your engine hot, if it's not the case (early in the morning or just after starting the engine) and you're noticing those surges then it's surely not the DPF recycle.

[jerrah]

random high idle. Normal idle is 600rpm,... it will idle at 900rpm. This causes the fuel consumption readout to go up .. All of this is without air-con on.

I'm 14,000km into MQ ownership and mine did this for the first time on the way home from work today. First time I've noticed it and I probably wouldn't have noticed except I turned off the AC and the idle speed didn't drop. The car felt hot but it wasn't any hotter than any other day (nothing out of the ordinary reported on the dashboard) The last three days I've driven in gridlock whereas I only usually drive on country roads at high speed or offroad. I figured that it was the DPF and after the road cleared out it was idling normally by the time I got home.

My fuel consumption on the dash readout shot up to 20L/100km during this behaviour!

I guess you'd never notice if you never turn off the AC?

[-ollie-]

Did any of you guys get an answer from Mitsuibishi on this? I've been having this exact same issue on my MQ. Has almost 14k kms now, started noticing it at around 10k kms shortly after I installed a DP Chip, so my fear was the chip was effecting the idle. It seems to be intermittent though (which led me to think it therefore can't be the chip that's on 100% of the time, unless there is something faulty in it), but obviously only noticeable at idle. I drive fairly regularly (at least once a month) 4-5 hours at 100km/h, I have a provent catch can, and have never had the DPF light on the dash come on to suggest that it's a DPF burn. I'd expect to see more fumes out the back of my exhaust if there was a burn happening as well, which I can't see at all. I also have a EDS which isn't showing any sensor faults. I was going to mention it to Mitsuibishi at my 15k service, but I saw this and thought I'd see what you guys managed to find out.
Cheers

[shawty950]

DPF light doesn't come on while a regen cycle is happening.
I have a chip on which triggers the DPF regen more regularly and only reason I know is that engine note changes, idle's higher, and ultragauge shows -ve boost to -3psi and the cat 3 sensor goes from 400ish to up over 600C...no light at all.

[ctan1968]

Hi Pelister, I have a second hand MQ with 112000K's on the clock and experiencing the exact same problem as your post with the idle speed at 900.
Have you found the fix for your problem?
Thank you in advance

[DibbyDibbyDJ]

It will be the car doing a DPF regen (burn) Nothing to worry about, as long as you are not parked on grass

[mitzi1]

I notice it was said, idling speed is normally 600 rpm. mine used to be but is now 650 after idling at 800 rpm for a short time after morning cold start with glow plug light coming on after turning the key to start. Glow plug light comes on regardless of temperature and the whole thing is over after stopping at the first corner, with idling speed back to 650 again. Any ideas please???

[ctan1968]

Hello all,
New to this forum. I have a second hand MQ which has done about 112,000Km and starting to show signs of high idle (900) where normal is about 650.
It has happened about 5 times and I thought it could be requiring an active DPF regeneration. The fuel consumption also increases during this time.
Sometimes it lasts about 24hrs then corrects itself.
When you first start the engine, it sits at 650 then within 20 secs it goes up to 900.
If it was requiring an active DPF regen, I have driven it for about 20mins at 100km/hr for nil result. I though this would surely complete an active regen.
I have used Liqui Moley DPF cleaner once.
Happens about 1 - 2 weeks apart.
Any guidance would be superb.

PS: I noticed that there is a similar post from 2016.....
Thank you all.
Chris

[NowForThe5th]

I noticed that there is a similar post from 2016.....

Which is why I've merged the threads. Let's keep all the same stuff together, please. Makes for much easier searching later.

[DibbyDibbyDJ]

I notice it was said, idling speed is normally 600 rpm. mine used to be but is now 650 after idling at 800 rpm for a short time after morning cold start with glow plug light coming on after turning the key to start. Glow plug light comes on regardless of temperature and the whole thing is over after stopping at the first corner, with idling speed back to 650 again. Any ideas please???

To start a cold diesel you need excess of fuel and heat. The excess of fuel would increase the idle speed to a point where the ECU knows it doesnt need extra fuel and therefore your idle speed returns to normal.

On old school diesels it just used to inject more at once. With modern common rail it just injects more times per stroke, which also helps with diesel knock when cold. MR Triton could inject 5 or 6 times per cycle to acheive this, and then revert back to 2 when warm

All normal operation

[mitzi1]

Thanks