MembersPage/RanzAudi (2010-11-24 16:37:33)

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.

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:

overrun-1.png

overrun-2.png

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

http://ranz.planet.ee/idle2.vemslog

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


Things to check...

but overrun_fuelresume=1800rpm (maybe not always ? Possibly not true for at all part of the log ?) and fuel back at 1173rpms

Other strange thigs:

Log analyse (http://ranz.planet.ee/idle2.vemslog)

Interesting thing after tps pulse (rpm falling) and pw:

I saw the modification around 22sec in the log (you can see the marker in the multigraph):


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

(Reidar, some of these were suggested in the tread already and is not what this wiki page is about, this page is about why overrun fuelcut didn't do it's job. All the config changes are in the log file, you only saw the first part with no overrun fuelcut - scroll and put the marker in the last blips of throttle and you will see the overrun fuelcut enabled, the marker from the config change is visible at the bottom of the log viewer.)

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. could try value: 70

I= Lower this value. Could try value: 3

D= Increase this value. A really High D often helps on cars with AirCond where they got stall issues when AirCon active. (just experience) Try a value of 150

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

I usualy tune it a bit rich on idle. 0.95 or so.