Uneven idle, mostly warm - and fault code ECM-250A upper limit

[SuperHerman]

I would also look at fuel trims for signs of an air leak. Plenty of write ups and videos on the internet to help analyze the data and to see if it is your problem.

What brand is the air filter - I had issues once with a cheap one I bought b/c the store stocked it - changed it for a quality filter and problem was solved. They all don't seal the same.

On your specific model year car I would also look at the MM throttle body.

[Orchid70]

Thanks abscate.
Found it strange that Vida doesnt log fuel pressure, only the tank pressure.

We have been driving today - so I logged some values of the lambda sensors.

First idle STFT and LTFT:

Same during drive:

Pre cat lambda and post cat lambda during drive:

Fault code came up again during following conditions - nearly the same as always before

Victor 200107.pdf

(43.8 KiB) Downloaded 24 times

What does it say - that it happened 4,6 minutes (279616 ms) after the start? That would been during idle. But the vihacle speed was 52 km/h??
I can see that the rpm gets lower and lower in the Freeze frames. From 2500 to 1250 today.

[Orchid70]

Something I noticed yesterday - back probing and measuring with oscilloscope....
I didnt turn off the MIL first.
The car run FINE - the rpm got erratic only if the coolant fan turned on. After it turned off, the engine got smooth again.
For hours, when I was trying to find right scales on the oscilloscope.
I also did propane test and vacuum leak test and the rear lambda sensor reacted fine.
AND - I have changed the first lambda in vain. I realised that the pre O2 sensor is a wide band sensor and CANNOT be tested the same way as regular lambdas. It always gives you steady 3-3,3 V line...... and it should do so.
Fine reading about this:
http://www.partinfo.co.uk/files/4%20Wir ... ensors.pdf

https://www.scannerdanner.com/forum/dia ... .html#2903

So - after some good time running at idle, I turned off the MIL - and the engine went straight back to its erratic fluctuations!
VIDA has no way of forsing the learnig values. Stupid Volvo.
After some searching I found how to learn new values for 5 cylinder non turbo.
From VIDA:

The rpm is high/low during engine braking to a stop. This is so because idle control needs time to learn how much air the engine needs when the engine runs at idle. The adaption takes place every time the engine idles. Only a limited amount of adaptions is allowed each time. This means that you have to leave idle every once in awhile for the system to finish adapting.

One way to do that is to run the engine warm and then let it idle. If the vehicle is equipped with automatic transmission, gear position D (drive) shall be used.

With some minute's interval, load the engine a little by revving it for a few seconds. Then you let the engine return down to idle.

Test-drive the vehicle to decide if the system has finished adapting or not.
END quote.
(All other learning procedures - search for "learn" and youll get the link - you can find this under "network" "ECM")

I have seen couple of mentions how to "force" the readaptation/resett: viewtopic.php?t=21123

The fault code always setts during initiall startup, in open loop. After erasing it - the MIL lits first after next time you turn on the ignition.
The idle is erratic only after erasing the MIL.
With MIL, idle is fine. Except when there is extra load on the engine.

[Orchid70]

An other question before getting off to resett the learning.....

This car gives STFT and LTFT in lambda.

Does 0,85 equal to -15%? (it cannot be 85!)
And 1,11 equal to 11%?
1 = 0

It would be so much easier if they would use % as every other normal car maker....

[RickHaleParker]

An other question before getting off to resett the learning.....

This car gives STFT and LTFT in lambda.

Does 0,85 equal to -15%? (it cannot be 85!)
And 1,11 equal to 11%?
1 = 0

It would be so much easier if they would use % as every other normal car maker....

International System of Units recognises two decimal separators, the point and the comma. 0,85 = 0.85 = 85%. The rest of the numbers above are written in the comma decimal separated format. Example 0,71 V on the rear O2 sensor.

[Orchid70]

This is not Volts - this is Lambda

Ive been adapting the car the last ½-1 hour.
Both STFT and LTFT stay close to 1. Between 0.94 and 1.04.
What would those numbers be in % - as usually are the STFT and LTFT presented?
I have never seen a engine have STFT 94% and engine speed at idle 750. It doesnt make sense.

Here the first rev with warm engine:

victor warmup after reset2.jpg (106.02 KiB) Viewed 337 times

AC on and some fluctuation:

victor warmup after reset5 electric load.jpg (103.83 KiB) Viewed 337 times

NOW - the STFT is moving and LTFT is steady =) Not like before, the other way around:

victor warmup after reset8.jpg (107.13 KiB) Viewed 337 times

victor warmup after reset9 learning perfect....jpg (100.43 KiB) Viewed 337 times

[Orchid70]

Engine light came back after 4-5 days this time.
Fault codes:
ECM 150A - MAF - upper limit - not active
ECM 250A - Long term fuel trim - upper limit - not active

I took a cleaned, known working MAF, from other car, but it in and did the adaptation procedure again. 4 days ago.
I have tried the other MAF before - but without doing the adaptation.
Lets see if this did the trick then.

[abscate]

Now you have the fault, measure the long term fuel trim again, let’s see where it is.

Trim values between 5-15% (0,85-1,15) are normal and won’t cause a code

[Orchid70]

Long term fuel fault code is ALWAYS sat at 1,40-1,48 (40-48%).
I was never able to dublicate it with Vida hucked up though.

This time:
MAF fault code first: Long term fuel: 40%
25 km later long term fuel fault: at 48%

victor 200113.pdf

(47.61 KiB) Downloaded 37 times

The issue here was - that the resetting of the ECUs needed to be done - at least with some vihacles. I tested this very same MAF already before.
Dont know when I can relax - and consider the fault been found. In two-three weeks?