Weird idle EGO corrections

[AVP]

Id like to make an observation....

I have noticed that although my VE is nicely tuned and fuel enrichment as well to compensate for audi's intricate issue of mixture becoming lean on idle as IATs go higher, and although most of the times im able to keep EGO correction between 99-101 on idle on various IATs, i have been noticing the following:

As sometimes i have been on a short cruise and my IATs are say 17-19C i stop at a traffic light and i see that EGO is going to 103 in order to keep my target lamda.

Then on a different day, same IATs, no change to the map whatsoever, and the ego is at 97 again to keep the same lamda...

What is the meaning of this? Could it be that sometimes the idle valve is sticking or not opening as much and therefore lamda needs to compensate?

i have a dedicated 4 bins on the VE table for idle, so the possibility of the VE map to be jumping from one bin to the other is not an option.

Engine going leaner on idle or in general, would that mean that there may be an air leak somewhere that is causing this, or is it the other way around?

thanks
Vas

[MWfire]

use IAT/TPS map for correction thise.
So at 0% TPS you don't want to remove fuel.

[mattias]

What MWfire said.

Consider that your current ambient IAT is the "baseline" where you don't touch the value in the MAT/TPS table, tune it so that as IAT rises, only add fuel at the corresponding IAT bins at 0% TPS, to get the EGO correction to 100 %.  From this you can probably figure out that adjustments made in the middle of summer probably don't work out too well in near freezing temperatures, so requires a slight retune.

As soon as you put load on the engine and move away in traffic the IAT sensor should fall back to the real reading. 
Unfortunately on some engines, the stock IAT sensor position is really bad. Example, on Audi S4 the sensor is just above and behind the throttle plate, but the flow of air is only at the bottom of the throttle due to a piece bolted to the plate, so it takes much longer than it would if the sensor would be placed directly where the flow from the slightest throttle opening crosses it.  On this engine in particular it can be a good idea to move the sensor in front of the throttle.

[AVP]

interesting thoughts and this is how i have dealt with the problem.

my question though regards when we are talking about the same iats on different day, or after a cruise or a traffic jam.

so for say 17C iat, i calculate and configure the VE values and after a few days on different ambient temps but same IAT, i get the mixture not being close to the already configured value!

its a small issue, but i dont get why VEMS would show that on one circomstance of 17C i had 100 EGO and after a few days on the same IAT, i get 103 EGO!!

[mattias]

3% at idle is nitpicking, especially when you consider the number of variables that can affect the combustion process and that the system only knows a few (those that really matter). A fuel temperature sensor can be pretty important, coolant temperature, fuel injector characteristics, etc.

[AVP]

Ok, I won't worry about it then!

[tweak]

Mattias interesting that you mention fuel temp sensor. Of course with low flow the fuel might soak heat from the engine and as we know the hotter the oilproducts are the less density it has. Also a hot injector might need increased PW to provide same amount.. But is Audi I5 the only engine that can encounter this? hm.