Idle mixture gets leaner the longer it idles

[corradophil]

Hi, just joined today

I have a VW Corrado with a 2.0 16v 4cyl and individual throttle bodies.

I am using MS1 V3, and it works well, with the exception of a problem at idle.

After a decent drive to get it up to full temperature, with no cold enrichment I can set the AFR at around 14.7:1, and it will run fine. However the AFR gradually gets more and more lean until it eventually settles after around 20 minutes, so I then adjust the VE table to get a nice idle at 14.7:1, take it for a drive, and the idle is around 11:1 AFR. Leaving it idling for 20 minutes brings it back to 14.7:1.

The air intake temperature goes from around 25 dec C when driving to 36 deg C after 20 minutes of idling.

I have experimented with the spark advance retardation based on AIT increases, and while it has an effect, it is not effecting the AFR enough to be causing it.

Is there a setting which will enable me to add fuel as the AIT increases or am I missing something obvious?

[lagos]

Take a look at the Mat air density table under basic/load table. By default this table follows the ideal gas law, which is good in theory but not in practice. I have gotten much better results by setting everything over 68F to 100% and then slightly dropping the correction to 99% at around 100F. Give it a try and see how this works for you.

Its also a very good idea to tune your injector dead times. If they are out of tune, then a 10% change in the air density table could be sending more or less fuel than it should causing even more problems.

[corradophil]

Take a look at the Mat air density table under basic/load table. By default this table follows the ideal gas law, which is good in theory but not in practice. I have gotten much better results by setting everything over 68F to 100% and then slightly dropping the correction to 99% at around 100F. Give it a try and see how this works for you.

Its also a very good idea to tune your injector dead times. If they are out of tune, then a 10% change in the air density table could be sending more or less fuel than it should causing even more problems.

I found this yesterday http://www.mez.co.uk/ms15.html and followed the procedure last night. After a lot of adjustments it is much improved.

I will take a look at the Mat air density table under basic/load table. I wasn't aware of it, but it looks like increased intake air temperature is definitely the issue here.

Injector dead times - This is something I have no knowledge of, so I'll do some research, and check it out