High Idle at 2 MPH

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Hi everybody,

New to the forum. I just did an LS swap into my 1972 Nova. I have been refining my tune, but could use some help. The car idles very happy in the 850 - 950 rpm range. However, when coasting to a stop the idle is quite high and rapidly falls off once I stop (back to a happy feeling idle). If I'm coasting to a stop shouldn't the idle come back down to a reasonable level?

Engine: 6.0 liter LQ4 out of a 2000 Silverado
Transmission: 4L80e
Converter: 2800-3200 Stall 10" lock up
Intake: Ebay Fabricated intake with 102MM throttle body
Cam: 1997-2004 GM LS Series (Gen III)
Lift: 0.585"/0.585"
Duration @ 0.050": 228?/230?
Advertised Duration: 283?/286?
Lobe Separation: 112?
RPM Range: 2,500-6,500 RPM

Currently I have the MAP sensor disabled!

I'm sure there's plenty of issues the members of this board will notice. Appreciate any feedback. Thanks.

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also uploading the CFG files according to sticky

[5FDP]

I only looked at a log but your idle timing is way too high. Does not need/want 30-32 degees for this engine. Try 18-20 degrees. I notice it comes down in timing and then spikes up to over 30 degrees around 3mph.

[[email protected]]

Thanks 5FDP. You're right, I did bump up the timing quite a bit here. It helped get this aggressive-ish cam running smoother (same as this guy: https://youtu.be/w6YTFH4LAmI?t=504). However, your observation helped me realize I did not do this for the base spark tables as well. They were quite different at this RPM. Bringing these into alignment and unifying the park and idle rpms helped quite a bit. I do realize I will still need to bring the timing down eventually.


Another problem is the IAC on my large 102mm throttle body was screeching at light throttle. Adjusting the IAC steps according to this video also helped.

https://www.youtube.com/watch?v=621bcy3Epzo