This audi 5cyl works, but experiences "idle fluctuation problem"

We've created this editable page to be able to help him, summarize the findings, suggestions in a thematically organized way.

The warmer the engine, the worse it gets.

The air seems not to make any difference

We've experienced that similar idle problems are often caused by VE table. Can be very sensitive in some cases. Because of the wideband measurement and EGO delay it's hard to diagnose properly (the leaning shows up later in the log than the actual problematic loadsite).

In many cases the idle fluctuation was cured when the VE was fixed at the right loadsite.

History - Mattias wrote on chat:



At that point, fuel should be resumed after overrun, shouldn't it?

Expression grid says ecu pulse width = 0, and so it is.. but the overrun fuelcut settings don't say so.


Important: In the log he tries at first with no overrun fuelcut, later with the ones in my screenshots.

Interesting thing after TPS pulse during engine breaking and RPM is falling, observe injector pulsewidth :

You can see the config change around 22 seconds into the log (orange marker in the multigraph, see picture above). Changes to overrun fuelcut goes from :

In the log the fuel resumes at higher pressure than 18 kPa and at much lower RPM than 1800 rpm. So the settings are not interpreted correctly. More like 25 kPa and at 1174 RPM, which is not intended.

Other observations on the configuration

Im going to change the MAT/TPS tabel, never paied any attention to it :(

What is wrong with MAT/TPS ignition retart?

Boost target is above, but real boost is under. In real life it does not go over 260kPa (stock K24-7000 turbo)

The log/config has some config errors which WILL cause idle problems.

(Reidar, some of these were suggested in the forum thread already. All the config changes are in the log file, look above how to see this)

IAC PWM Frequency: is set to 250hz. 25hz works fine on the audi aan/aby/adu/3b

Set the whole idle area in the Ignition table to the same ignition advance.. 15deg on idle or so.

The PID settings is somewhat off in my opinion and experience with these cars.

P = Increase this, try value: 70

I = Lower this value, try value: 3

D = Increase this value, from experience a really high D often helps on cars with AirCond? where they got stall issues when AirCon? active, try a value of 150.

Use the ignition based idle control to get a steady idle.

I usually tune it a bit rich on idle. 0.95 or so. - Reidar

IAC PWM Freq was @25Hz when there was no diode @ valve cables and the valve made disturbing click noise, after adding diode I raised it to 250Hz and that worked a lot better. As I recall, the problem was same before installing diode.

Ignition is set to 15 all around IDLE.

Ill try changing PID settings next week, for now I am away from the car.

I dont have a log file from my own car, but just installed one ECU to audi S4 and it had same problem with the idle (same 1.1.81FW and almost same conf as my own car).

Tried different things:

Lowering IAC PWM Freq did not help, back to 250Hz.

Higher P, lower I and higher D did not help also, it got worse... the idle jumped up and down over 5 seconds before stopped @850RPM.

Using Ignition based IDLE did not help also, no difference at all. But what helped... using all other settings but incrising D from 1 to 100 :) now the car does not drop below wanted idle RPM more than 20-30RPMs :)

Ill now try it on my own car also and make a log from it.

Start tuning the P in the pid settings. Increase untill the engine revs up to a little (50-100rpm) above preferred RPM value. Now it will probably be pending up`n down and wont settle at the given RPM.

Set the I' to: 1 or 2

Enable EGO if you want.

PS! this might not be the correct way, but it sure works for me!


Thaks for the help tutorial, but that did not work for me. I disabled EGO, locked ingnition and set PID to 0. Now changed the IAC ref when I got IDLE wat I wanted. Now revving up it catched the wanted RPM pretty good??? the RPM dropped somwhere 750RPM and catched 850 target pretty well (ignition lock disabled).

Now I tried to increase P, 10, 20, 50, 100, 200, 255... nothing, the RPM stayed @ its position. So I put it 50 at first (aftewards tuning other fields lowered it to 30, so it worked better).

I to 2 and D to 170... ignition based idle control enabeld as you sugested and now it seems to work pretty well:)