Logging KR and stumbling shortly after startup

[truckfan2]

I am working on a LQ9 in a Tahoe with a sloppy stage 2 cam, longtubes, and a 90mm TB. Overall it runs decent but I am having some afterstart issues. When its cold (sitting in 65 degree shop overnight) it fires right up and idles great. If you simply wait a few minutes and try again it starts, stumbles for several seconds, then starts idling good again. Basically its a 2nd cold start issue as the ect can still be reading 80 deg. when I try the second time. I am also logging some KR during the stumbling idle period as well which I have never seen. I have been adding some friction and startup air trying to get a nice strong fire up but not really getting anywhere quickly. Log and scan attached and any help would be appreciated.99 silverado 6.0 jason Clark monster blazer initial iac reset to 220 AC changes10.hptBlazer start up issues.hpl

[kevin87turbot]

I am working on a LQ9 in a Tahoe with a sloppy stage 2 cam, longtubes, and a 90mm TB. Overall it runs decent but I am having some afterstart issues. When its cold (sitting in 65 degree shop overnight) it fires right up and idles great. If you simply wait a few minutes and try again it starts, stumbles for several seconds, then starts idling good again. Basically its a 2nd cold start issue as the ect can still be reading 80 deg. when I try the second time. I am also logging some KR during the stumbling idle period as well which I have never seen. I have been adding some friction and startup air trying to get a nice strong fire up but not really getting anywhere quickly. Log and scan attached and any help would be appreciated.99 silverado 6.0 jason Clark monster blazer initial iac reset to 220 AC changes10.hptBlazer start up issues.hpl

The IAC is in the 210 range at idle. You'll need to open the throttle body to get the IAC in the proper position at that idle speed. Typically in the 40-70 range once it's at operating temperature.

[truckfan2]

The IAC does end up dropping down under 100 once it warms up. Also if you watch while its struggling to grab a good idle the IAC isnt jumping up or anything crazy like it cant get enough air from it to correct the idle.

[kevin87turbot]

The IAC does end up dropping down under 100 once it warms up. Also if you watch while its struggling to grab a good idle the IAC isnt jumping up or anything crazy like it cant get enough air from it to correct the idle.

Does it help it to start quicker if you crack the throttle open? If that helps, then it likely just needs a little more airflow. If the IAC drops to just below 100, I would recommend opening the throttle just a bit more to get the IAC in the proper operating range. If that doesn't fix the issue, you can drip the IAC opening just a bit as well.

[truckfan2]

I have played around with the friction airflow and startup airflow and it starts decent now. Its still pretty weak at startup then ramps up to the commanded idle after a few seconds. Do you generally use startup airflow or friction airflow in a situation like that? What are the park position airflow numbers for?

[kevin87turbot]

I have played around with the friction airflow and startup airflow and it starts decent now. Its still pretty weak at startup then ramps up to the commanded idle after a few seconds. Do you generally use startup airflow or friction airflow in a situation like that? What are the park position airflow numbers for?

I get the IAC adjusted first. After that, the Startup airflow table will help get it started up.