Euro 550 OBD plug . Yes it is there and I have found it.

Yesterday evening I looked into both the TPS's. The left ECU (left TPS??) showed a higher max, at around 72 %, starting at 0.8 depressed.
The left TPS position is easily checked by looking at the throttle cable. It had more slack than I thought was needed.
So I tightened the cable a bit (the 2 13mm nuts construction) and now the max is 78 when I really floor it, still starting at 0.8%.

The right side now is around 72 instead of 65 due to the tightening of the cable, but still starting at 0%
On other cars a TPS has oval slots for the mounting screws, so one can tilt it a bit to a side to adjust the values, but these TPS's seem not to have that.
.
Other thing about the TPS, both sides show a nice and smooth graph on the scanner when I slowly press the pedal, no spikes or hiccups. So they seem to react as they should, only if the starting is 0.1V or 0.4V I do not know. I understand that the range should begin at 0.4 - 0.6 volts , up to a max of around 4,1 and higher.
But I am a bit hesitant to remove the big connection on the ECU and still have ignition on to check that, but if it is necessary I will do so.
Not being near an SD is indeed limiting what one can scan.

As both TPS react smoothly to the pedal, and have comparable values in comparable situations, I do not think they are part of this problem, but again, I am not sure.
The stark hesitation when driving feels as if it is on 6 cylinders for a short time, so a value must really be off when that happens.

I will check for vacuum leaks. I have already sprayed brake cleaner around the manifold, but no effect. I will try with the smoke machine next.
But then as well, as far as I understood, vacuum leaks have more effect on idle than on full throttle situations at 3500 rpm.
And the LTFT did not come down from 16 after 5 minutes at 3500 highway cruising in 4th gear...
The IAT is showing a correct value on my scanner, as is one Coolant sensor (other is showing -40)

2 symptoms I just thought of that also occurred:
- when the hesitation occurs, and I shift up or down, often it is gone for a few moments, it picks up the next gear smoothly. And that points to a TPS or MAF (0% during shifting), right?
But no strange values of the right TPS during this.
- I stopped for gas, but the car stalled before I turned off the engine. On 6 cyl, it will not stall, correct? So if one of the fuel pumps temporarely cuts out, it will not stall? (When I collected the car 6 weeks ago, and the new right fuel pump stopped working during the drive home, it did not stall)

I think I will start with the parts throwing if the smoke turns out no major leak, and the TPS voltage at the pins is good.
The left tps is cheap, the right not really so at around 350 usd , but I can buy a used one from a fiat/lancia breaker at 75 usd. So at usd 100 I have one part out of the equasion.
I have no idea otherwise except for the MAF's.
Other sensors on the car, the 2 underneath at the flywheel, can they have this effect?

 

Had ran out of baby oil (not what you think), so the smoke test ended well before it was really started. (the baby oil is very convenient for the smoke machine)
In the minute of filling the system with smoke, before I ran out, no traces visible. But have to repeat that after visiting the grocery store.

So what else to do, except for disconnecting the ECU connectors? Well, why not check the MAF values to each other. So placed them back and reconnected everything.
I knew the left MAF started at around 4-5 , which is normal for a 2.75 liter engine bank. (rule of thumb approach).
But as I did not know the value of other one, I made a graph to see if the line was nice and lineair.
Well, this is what came out after I ran the test on both sides, from 950 rpm up to 2400.
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Looks like the right one is more or less ok, but the left certainly is not, even if it starts out ok . But a dip in the value is certainly not good.
So I am really happy that I have found something that is not right.

Next thing to do is order a new one, and compare further! Maybe the right one is too high or maybe still too low, having a more or less straight line is no proof...
Thanks all for help and suggestions, will report further when the new MAF has arrived.

 

I have disconnected both MAF's at the same time as well before decided to write down all values, but as it is running too rich by default when the MAF's are disconnected, it was not really clear that it was an improvement. I did not take it for a ride, but checked it in my garage. Maybe a test drive will indeed show improvement
Tomorrow will be a rainy day I understood, so no testing outside.

What I can do tomorrow is switch the MAFs and see if the low values follow to the other side. Pretty handy, almost everything double on this engine! Free testmule!

@franschman, thanks, very kind.
Living in The Betuwe, between Utrecht en Den Bosch...
But I am positive that my test tomorrow will show that one MAF is faulty. If not, maybe if you are relatively near, we can arrange something!

 

Ok, did a testdrive with the suspected bad MAF disconnected. The expected good one still connected.
The car did not drive well, not much power, hesitating, even got a Slow Down Light for about 10 seconds!!
Really can't see a connection between the SDL and the MAF or any other sensor...
When the SDL disappeared, the car regained power for like 3 seconds, before it felt very sluggish again, even though the SDL did not return.

Back home I connected the scanner, TPS's still react normal to the gas pedal, so that information should have worked well as input for the ECU instead of the MAF.
I also checked the output of the O2sensors, they switched nicely between 0.1 and 0.9V so that looks ok. Only the secondary O2 sensors showed a strange pattern, but as far as I understand they do not control the air/fuel mixture. (or am I wrong here?)
Right now I am out of ideas what to check or do, other than the full smoke test, but as the LTFT came down to 10 (no idea why, last time it remained at 16...)
it can't be a self-closing vacuum leak...and the hesitation is mostly felt at half and full throttle, where vacuum leaks are the least influential...
So even if I find a leak, it is not likely to be the cause of the sluggish and hesitating power.

Any out of the box ideas?
Sticking butterflies, how can I check that? Open it up? Does it have 12 butterflies or just 2? (I mean, are the valves/butterflies in the manifold as well, I know of the two on the side)
As it is purely mechanically connected, would I feel it in the pedal? (felt nothing so far)
How about the variable length manifold sensor?

 

Ehhhhhhhh, no? The left ECU gave the low MAF readings, so I disconnected the left MAF....I should have disconnected the other one?
Can try that hopefully today.
Other test I will try , is do a test drive with the fuel pressure tester, and the gauge itself taped to the windscreen. So I can check live fuel pressure , to see if it drops below a certain level.
Anybody any clue what normal minimum on psi I can expect?

About thermocouples, I had a faulty one on my 355, that caused a SDL even starting from cold. The 5.2 ECU had stored the values, even though the thermocouple values were not strange when cold.
It turned out that one was misreading the increases, it only showed 10% of what it should do, so at operating temp the difference between left and right was say 1.5V, in any case enough to throw the SDL on my 355 which it showed even when I let it cool down and start from cold the next day.
If I had more SDL's in my 550 it could well be a broken thermocouple wire, that sometimes gives a good value, sometimes not, causing the ECU to go into limp mode. But that would certainly have the SDL solid for most of the time? The SDL from yesterday was the only time, and it lasted maybe 10 seconds before it disappeared, but the symptoms kept coming and going. Very odd.

 

Small update,
The testdrive I could not do, because the pressure tester started to leak before I drove off.
But I was able to rev some with the hood open, with a canister beneath the leak. Dangerous, I know.
But it showed a (what I consider) normal behaviour: idle at 50 psi, and with a bit revving to 3k a drop to around 45 psi or so. (remember it leaked, so without leak a few psi higher)
The hesitating , low power symptoms occur at all driving speeds, already with only slightly opened throttle (or at least the pedal), so I do not expect that driving conditions suddenly see it drop to 20 psi or so.
What I did notice with the right side MAF disconnected, standing still, and revving slightly, is that the revs of the engine fall back a little when holding the pedal steady to achieve a certain rpm. But that could be because of the disconnected MAF, not sure. Or an indication of a failing TPS...
I did not do the testdrive without the fuel pressure , my time was limited. I can't really say if the engine sounded better with the maf disconnected.
A used (reportedly good)MAF is on its way, as well as cheap new reproduction parts, so I will check further with those parts. Just as long as it takes till I get equal, logical readings from both sides. Later this week I assume.
Hope to resume the smoke test this evening.

Then something completely else, I read of the green check OK light that it should show (in the manual and here Fchat), but my car never shows a green OK.
I have seen all sorts of info, like doors open in red, the SDL in red, triangles underneath the wheels in amber, Fuel sign in amber, ASR in amber.
But nothing in green. Even the outside temp button shows me the temperature in amber...
Is this a sign that the car knows it has a problem somewhere? But no codes on the scanner...
Or do more cars miss the green OK? And is this not related?

 

Hmmm, the only message I get is the amber colored triangles (which disappear after driving off). No Check OK in any color...which I understood I should have had regardless of the actuator message.
I have had the car for 7 weeks now, so I do not know how it was before that.