Troubleshooting my 2008 mk7 3.2L "luton" engine/electrical

[Sports140]

Hi!

Got my hands on a well worn but not too bad 2008 3.2 mk7 350E box van some months ago. I've only been using it a bit so far, maybe four-five days a month on average, and had many other repairs on my other vans ahead in the queue, so it's been waiting on me a bit
Now it's about to get put into more steady use, and I think I might be facing a multifaceted issue, so thought I'd throw a line out here to see if anybody has some good insights that might save me a day or two (or four) in the troubleshooting
(I'm perhaps a low-intermediate level DIY apprentice, to put it that way;)

So, my current main issue that I'm looking to cure is a very unstable idle. It starts smoother, but gradually get's more and more "wavy", with the engine midly revving in pulses. RPM, FRP, MAF, MAP and commanded EGR all follow these wavy pulses in sync afaict when observing with forscan (haven't looked at the VNT data yet, might include that next time).

After a short drive getting the engine to temp, then letting it idle without having turned the engine off (not tested if it works the same if warmed up, then off and on again before idle), it seems to idle quite smooth, but gradually these waves start appearing and becoming more and more prominent.

Previously (knock on wood) there was an issue with "kangarooing" on cold start, ie the van would move in "leaps", so to say, when driving cold in low gear and low acceleration (I think it maybe went away if it you hit the pedal and got the revvs up, but only half sure about that now), which would seize to happen once the engine was warmed up.
Last night I replaced the diesel filter (mann) and air filter (both looked due), plus gave the MAF sensor a good clean with crc maf spray (it was looking a bit black and oily in there), and today the kangarooing seems gone (though I did let it idle a couple minutes before driving).

There has also been an issue with the van getting a red "engine malfunction" warning when driving sometimes, and going into limp mode. This would always (afaik) go away if you turned the engine off and started it again, though it could come back later. The previous owner said he would usually just clean the MAP sensor with some diesel when this happened, and be good to go.

Other possibly related symptoms is the odometer display panel often going haywire (upside down, abstract art, completely blank etc) and shows a "oil change due 0 miles" alert in swedish that's always there on startup (though I can see in forscan that the service intervall has been reset, and the miles since last oil change in there is very low).
The ambient temperature sensor appears dead and has a present DTC for circuit voltage below threshold. Another present DTC is a short to ground on left licensense plate light. Previous, not present DTC's, for brake pedal switch "B" signal stuck high, and overboost + actuator stuck high on turbocharger "A". Finally, there is a series of DTCs on the EGR, including an obdii of confirmed malfunction on EGR vacuum regulator solenoid circuit. I could upload photos if wanted

Luckily, I have lots of spare fresh bits, various sensors etc (SCV, MAF, MAP and some, though I don't wanna replace functional bits ofc, but could be handy for troubleshooting at least, and great if actually needed

I'm thinking of either going down the route of SCV and EGR, or start on the electrical end. I guess the unsteady pulsing idle is most commonly an SCV issue? Would it also drag all the other systems along then?
Funnily, I read one bloke said he had that, or a similar suite of symptoms, cured by fixing a bad brake sensor.

Any ideas? Best place to start?

Cheers, McGilvray

[Sports140]

Think I might start on the EGR route, SCV second.

Does anybody know how bad or risky it is if you get a failed pump learn, and continue driving the van on "temporary" learn status?

[metalworker0]

This ambient temperature sensor .. is the one under the bumper somewhere or is it in the air intake, if i the air intake, its called a air intake temperature sensor and directly effects the running of the engine, if failed, specially at different temperatures .

all the best.mark

[Sports140]

Oh! That's very interesting!
I think I'll start there then, as it seems a smaller task, and would be good to cross off the list early

Thanks!

[knobby1]

This ambient temperature sensor .. is the one under the bumper somewhere or is it in the air intake, if i the air intake, its called a air intake temperature sensor and directly effects the running of the engine, if failed, specially at different temperatures .

all the best.mark

AIT (Air inlet temp) sensor is part of the MAF sensor and is screwed into the inlet pipe from the air filter to turbo inlet...the Euro-4's don't have a separate AIT sensor.

Lord Knobrot

[knobby1]

Oh! That's very interesting!
I think I'll start there then, as it seems a smaller task, and would be good to cross off the list early

Thanks!

Hunting idle will be the SCV not happy, either replace it and do the learns, you can actually pull the SCV apart and clean/polish the piston and it's bore.. It is the piston sticking in the bore, (Hysteresis), causing the hunting.

If the learns fail you may have other issues, poorly injectors etc.. What are the injector correction numbers..??

EGR has nothing to do with the learns failing.

Lord Knobrot (Smithy)

[Sports140]

Yeah, thanks knobby. I investigated a bit, and I believe the ambient air temperature sensor in question with a dtc is the one that's behind the bumper, sitting on side of steel chassis on right hand side. Easy to see when leaning inn over the wheel.
Probably not serving any other function than telling you the air temperature outside. Right?

I guess the sensors Mark was reffering to, which impact engine function, are those monitoring air intake temperature; one on the MAF and one on the MAP I believe. In any case IAT and IAT2 in forscan, both of which have good readings on mine.

I'm gonna try swapping the MAP for a new one (ridex, cheap, but it's a fairly basic sensor afaik) just for fun
Though previous owner linked "engine malfunction" warning and concurrent limp mode to the sensor, so maybe I get lucky

Do I really need to disconnect the power completely at battery terminals to swap say a MAP or MAF sensor, or is that more of a superstitious "anything can go wrong" belief?

[Sports140]

Thanks Knobbers! Back to plan A, reshuffled with SCV first then maybe EGR later. It's probably worth investigating the state of it given the DTC, and I'm not sure if commanded position really aligns with actual position.

When the inlets get cleaned further down the road I might just get it mapped out, and make or buy a couple blanking plates

[metalworker0]

Far as I know all sensors are dead with ignition off.

all the best.mark

[Sports140]

Thanks Mark! I've always thought it was harmless detaching and re-attaching such accesible sensors with the battery connected, ignition off, but it's nice to get some confirmation (and just throw it out there in case somebody knows a risk I'm completely blind to

Anyway, I did my "just for fun" swap of the MAP sensor for a new one, connected my forscan (good to run a data capture for future comparison etc) and fired her up. As (unfortunately) expected, no change. Ran smooth for a couple seconds, and then lost it's cool, gradually slipping into further and further unbalance.

In the spirit of "why not", I thought to do it with the MAF sensor as well (also because it's almost 1AM and I don't feel like getting into taking apart the whole intake side at this point;). When taking the MAF off for a clean yesterday, I either noticed, or caused, one of the two old rusty screws holding it in decoupling it's head from the body, so upon intallation of the new one (Astemo, japanese brand, don't really know anything about them) I also used a long fat plastic cable tie on the side now decidedly missing a screw.

To my great astonishment, the van didn't start the gradual wobbling off course, and actually idled really fine! The first three or four minutes were so spotless I thought I had accidentally solved it. However, the uneven idle started sneaking in over the next five minutes, though a lot more gradual and subdued than before, so I'm partial to a sub-par MAF sensor having been part of the issue, and will leave the new one in for now.

I did notice another thing; that the voltage at battery "B+" was also swinging in sync with these engine pulses, giving me a brief sherlock moment before I realised that the RPM swing would probably just be causing that via the alternator. So the SCV is on the menu tomorrow after work, still

Forgot to address previously, My Knoblord, that I haven't looked at the injectors at all really yet, save a glance at cylinder balance, which seems imperfect but not distressingly off (within perhaps +- 2.5 if I remember right, potentially acceptable for an old workhorse, but maybe not healthy enough to do an injector learn(?))
Were you thinking of if the correction factors matched the actual injectors, or could you divine something from just the factors themselves?

I'll have a look tomorrow evening and update here

Cheers, McGilvray

[knobby1]

When the inlets get cleaned further down the road I might just get it mapped out, and make or buy a couple blanking plates

Blanking the EGR will be pointless if you get it mapped out, it will be permanently closed anyway.

Lord Knobrot (Smithy)

[knobby1]

Forgot to address previously, My Knoblord, that I haven't looked at the injectors at all really yet, save a glance at cylinder balance, which seems imperfect but not distressingly off (within perhaps +- 2.5 if I remember right, potentially acceptable for an old workhorse, but maybe not healthy enough to do an injector learn(?))
Were you thinking of if the correction factors matched the actual injectors, or could you divine something from just the factors themselves?

I'll have a look tomorrow evening and update here

Cheers, McGilvray

Anything over +/- 1.0 is cause for attention....the higher th number the more difficult it is for the system to compensate. +/- 2.5 is not good and may be bad enough to cause the learns to fail.

Lord Knobrot (Smithy)

[andz327]

apologies if you've already mentioned but have you done all the learns??? can make a big difference without firing the parts cannon at it

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