topcaten

So some weeks ago I was driving on the high-way about 150 km, when stopping for coffe I had high idle - no CEL.
Scanning I had P1136 stat, and later P0507 int and after some more drive (not at the same time), CEL/MIL.
My MVB 032 (LTFT?/mixture adoptation) was +9% (idle), -13.3% (partial - load).
-> Had the car to the mechanic which apparently found some vaccum leak near som O-ring, which was fixed - also a elbow-pipe I had under the PRV was changed and I told him to change the fuel filter, since I wanted to eliminate that, and that had some 40'000 km on it - due for replacement. They also cleaned the TB.

Grabbed the car, but just letting it idle a few min, I noticed the idle was a bit high (maybe 900 rpm), but thought maybe I needed to drive and adopt - well no, idle got higher and higher back to the about 1100 rpm it hade before while driving the 50 min from the mechanic. During this drive, at least as I remember, when pressing the clutch the idle went down to normal idle, then 0,5 sec later up to 1100 rpm...

Own investigating
I didn't know if they adopted the TB, so I disconnected the battery for 10 min+, and think I managed to do a TB-adoptation.
Clearing codes, the engine runs more rough - I, who am not a mechanic, thinks it feels like some missfires (but my OBDeleven does not show any missfires count in MVB). As it adopts, those 'misfires' become more seldom.

Read that maybe the lambda could have something to do with this, so after about 10 km drive:

• MVB 033
  • Lambda control sensor 1: +25%
  • Lambda sensor 1 voltage: 1.6 V (static)

During the drive, lambda sensor moving towards 4.3 V during engine breaking, and around 1 V with WOT.

I'm not sure if immediately after this drive, or a later one, my MVB 032 was +9% (idle) and -11.7% (partial) - the idle is identical to the one before, and the partial is not - I'm not sure if that indicate that some of the things done to the car has improved the partial-situation, but not the idle-situation? Or that I haven't driven the car that hard, although I did some WOT-drive.

- clearing codes, stands stationary (at op temp)
At start-up: Rough as before (feeling those 'missfires') - LTFT is 0%

After 3-4 min rpm rises from 740 to 920-960 rpm

• MVB 032
  • Idle: +3.8%
  • Partial: 0%
• MVB 033:
  • +25%
  • 1.68-1.7 V
• MVB 037 Sensor 2
  • 0.05-0.055 V

After total of 11 min, rpm rises to 1040 rpm

• MVB 032
  • Idle: 5.8%
  • Partial: 0%
• MVB 033
  • 21.9-22.7-27.3% (27% is out of spec according to the OBDeleven app, it says max +/-25%)
  • 1.58-1.6 V

It would seem that the high idle maybe is not a result from when hot (which I thought), but instead from LTFT-being changed?
-> Any ideas to what my issue is?

Should the 02-sensor percentage be maxed-out, and the V so static, from what I read (no necessarily related to the 1.8t and BFB, the volt for 1st 02-sensor should move during idle (mine don't, but i can change from drive to drive to a different static level - i.e. voltage level)?

Also I tried consulting ChatGPT (3.5) it said to also consider the IACV - idle air control valve - does mine car has this?

Some parts that has been replaced quite recently (last couple of years):

• Brake booster (not OEM)
• PRV (not OEM)
• PCV? (not OEM) - they guy connected to the T-pipe under inlet
  • Also the T-pipe (not OEM)
• L-formed breather tube to block/case (under inlet)
• .. and as stated above, the elbow-pipe right under the PRV (hockey puck)
• Spark plugs last year (the expensive ones)

Based on this and that the mechanic has check for leaks, I guess that might not be so likely although I understand that's really hard to find them.
I run 95 octane here now, at the first sign of high idle (when stopping for that coffe), I was running 98 octane.

Any help is deeply appreciated, I have and OBD eleven if you want me to check some more values, although I don't think it can logg values over time...
Again many thanks in advance!

The car: Audi A4 Avant (B7), MY2008, 1.8t (BFB) FWD (it got 240'000 km on it - the car is stock as far as I know and 'feel')

UPDATE 230815
So today starting up the car I thought it would continue at high idle, since that was what it was doing yesterday with staying idle and stationary - but no.
It idles at normal rpm, I drove it into town, drives normally, except at a red light, where I thought it was some hesitation acceleration from low rpm. Parking it still normal idle, and now the MVB 032 is not at 0 - as stated above. Starting it up after my haircut, normal rpm and MVB 032 now at:

• Idle: 6%
• Partial: -5.5%

Driving home, still normal idle, MVB 032at:

• Idle: 9%
• Partial: -13.3%

-> Exactly the values before the mechanic, seems that what we did, did not effect MVB 032-values.

I also tried:

• Disconnecting MAF after clearing codes - car runs worse, almost wanna stall
• Trying to open oil cap while running idle - that's impossible (at least w normal force) - think I have been able to do that years ago (last time I tried) - at that time I also think it almost bounced on it's place if left untight

I don't know, high idle does not seems to be related to MVB 032? And also not warm or cold - but instead after time been driven or time at idle?!
-> What's next?

topcaten

SOLVED 230903

Both the PRV and PCV (which was chg before, but not OE) was changed to OEM, and the cars now idle correctly.
From what I understand from the mechanic, the PCV was stuck.
MVB 032 now:

• Idle: -0.6%
• Partial: -10.9%

But partial still seem to indicate some other problem, I'll do a new thread about that.