DBC Cold Start Issues L59

[MorPwr]

Hello!

I've been working on adjusting my base tune from PSI for an L59 out of a 2006 Silverado with a DBC Throttle Body. I have the fuel trims in a good spot, but the car does not do well after a cold start. If I give it any gas at all it will start to stall. I've been working with the base running airflow and IAC effective areas, but am getting some strange behaviors.

When I let the engine warm up after a cold start, the idle desired airflow will settle around 17g/s. If I immediately restart the car it will drop down to 7.

As a whole my idle desired airflow is consistently about 2x higher than my dynamic airflow on a cold start. This is throwing my IAC tuning way out of whack as the corrected graph wants me to change 200steps to somewhere around 400 steps. But as soon as I restart the warm engine, everything is right in line with where it should be.

Can anyone help? The log attached shows a coldish start and then a restart once warm. I have also included the tune.

Engine is installed in a 2004 Land Rover Discovery II

Thanks!

FullLog3_12.hpl
Disco_Updates.hpt

[Alvin]

I'd worry more about STIT and LTIT than what dynamic airflow is doing. They are really separate systems completely and do not have to match.


Have you tested the IAC? i've been seeing a lot of bad ones for the past 5 years so so. The way I check is pull up the scanner controls. Purposely drive the IAC to 128 (highest it will go in scanner) then to 0 and make sure the idle follows.

The ECM will drive the IAC but has no idea if the IAC actually moved or what it's real position is.

[MorPwr]

Well it certainly seems like you are correct @Alvin. Went into VCM Scanner and set the IAC to 20 and it ran just fine. Bumped it up to 30 and it was high. Seems like it was in complete la la land from what the computer was telling it. Will be interested to see how it acts on the next cold start, but that was definitely helpful.

[MorPwr]

Just wanted to follow up and say thanks again. Replaced the IAC valve with an OE ACDelco and everything looks perfect. Good to know that it can make IAC corrected look very, very wrong.

[Alvin]

Awesome. Glad you found it.

I'm seeing a lot of failed IAC's these days.. Seems to be about a 15-20 year life limit on them.