Coast Down idle jumps

[XPS]

I have an 06 C6 with a small cam. The tune seems great, it runs well, no surging, bucking at low speed, pulls hard all the way to redline. Everything seems good except for one thing...well...one thing that bothers me...not necessarily a problem.

Whenever I am slowing down, if I clutch or go to neutral, the RPMS instantly drop to about 900-1000 (current idle speed) then bounce up to 1300-1500 and falls very, very slowly, and wont come all the way back down to 900 until I come to a complete stop. I tried adjusting airflow, timing, etc in the idle range, but nothing I did seem to change the issue. Everything else seems fine...anyone seen this before?

[Ben Diss]

What's probably happening is that the desired idle RPM is being reached quickly and overshooting slightly. Idle proportional adaptive is kicking in too aggressively causing the idle to jump back up. The inverse is happening trying to bring it back down.

Try this.

Under Engine/Idle/Idle RPM

- Idle Proportional Airflow vs. RPM Error: In the coastdown row, left of 0 RPM, set all values to 0. Right of zero, multiply all values by .5.

- Idle Adaptive Airflow vs. RPM Error: In the coastdown row, multiply all values left of 0 by 2, multiply all values right 0 by .25.

If that makes a difference, put the old values back and verify what you think you saw. Then go back and play with different multipliers and see what works for you.

Post your tune and a log file of this when it happens and we'll be able to offer better advice.

[ktoonsez]

XPS
Thats good advice from Ben that should work for you, if it doesn't help it might mean the minimum airflow values are too high and it can't get enough timing out due to the high airflow.

[WarWagon]

Yes.
http://www.hptuners.com/forum/showth...977#post128977

[XPS]

What's probably happening is that the desired idle RPM is being reached quickly and overshooting slightly. Idle proportional adaptive is kicking in too aggressively causing the idle to jump back up. The inverse is happening trying to bring it back down.

Try this.

Under Engine/Idle/Idle RPM

- Idle Proportional Airflow vs. RPM Error: In the coastdown row, left of 0 RPM, set all values to 0. Right of zero, multiply all values by .5.

- Idle Adaptive Airflow vs. RPM Error: In the coastdown row, multiply all values left of 0 by 2, multiply all values right 0 by .25.

If that makes a difference, put the old values back and verify what you think you saw. Then go back and play with different multipliers and see what works for you.

Post your tune and a log file of this when it happens and we'll be able to offer better advice.

I only see Adaptive Idle Proportional Vs RPM and Integral Vs RPM. Are these the two you mean?

[Ben Diss]

I only see Adaptive Idle Proportional Vs RPM and Integral Vs RPM. Are these the two you mean?

Yes. That's right.

[XPS]

Here's a log and tune file for you, Ben.

[Ben Diss]

Couple things. The spark tables look a little wacked. Set the base idle and coastdown idle back to stock. Change you high octane spark table, in the idle regions, back to stock.

This could be the problem.

[LazMan]

I agree with Ben. I also noticed that your Main Spark High Octane has LOWER timing than your Main Spark Low Octane. Thats never worked well for me.

I made changes to your High Octane Spark Table and to your Idle Coastdown Spark table as well.

The table on the left is the High Octane Spark Table. The right is your Idle Coastdown.

If you made your change to the high spark table in order to get rid of knock when you take off gently, then consider lowering BOTH the high and low octane tables equally, and leaving the coastdown table as-is.