High Idle Right After Cranking

[ferocity02]

Have a minor but annoying issue with my tune. When starting the engine cold, the idle will jump up to 1500-1900 RPM, drop to 1100-1300 RPM, jump up again 100-200 RPM, then finally drop to the correct idle speed. It does this in a matter of 2-3 seconds. It does not seem to do this when warm, or if it does it's far less noticeable. I figure I need to adjust the start-up airflow under the Engine Calibration > Idle > Start-up. The vehicle is a '01 Silverado 5.3L with a T56 swapped in.

Perhaps the values in this section are more geared to an automatic transmission than a manual? They do vary quite a bit from an F-body manual tune.

My PCM thinks it's in 2nd gear during start-up, so perhaps it's adding too much air/fuel to overcome the drag of the auto trans that isn't there?

Anyone have some tips?

Thanks a ton!

[ScarabEpic22]

Im betting its because the PCM thinks you're starting in gear.

Not to beat a dead horse, but are you SURE you cant add the park/neutral switch to your setup so the trans can accurately report current gear to the PCM?

[ferocity02]

I probably can, but I don't think it's worth the hassle. Especially when I may go back to auto in the future, not sure yet. Many people have done the same swap and are using the 4L60E tune, albeit with some modification. The tune is pretty good driveability wise, there are just some minor things that need adjustment.

[ScarabEpic22]

Alright, just saying that you're tracking down issues that simply wouldnt exist if you ran the few wires the PCM needs...

What are your throttle cracker/follower tables set to?

[ferocity02]

Here are a couple logs. 0013 is where I started it a couple times this morning, but it didn't do it as bad of course. Then 0012 is a long log but the issue can be seen in the startup at the beginning.

Throttle cracker shouldn't be active, the activation speed is 3mph. I haven't messed with throttle follower but I'm guessing it too is not active during cranking/start-up since there is no change in TP.

One thing I notice is that the cat lightoff timing retard is starting before the idle has dropped to normal. Could this cause the engine speed to jump up?

Also, in 0012, the timing hits like 33* during the second spike in RPM, thought that was strange.