Working on my idle tune

[blsnelling]

It's still looking like I've got my In Gear idle tune nailed down pretty well. However, when I put the truck in Part or Neutral, the RPMs jump, and fluctuate between 800-900, even though I have the desired idle set to 650. Would this be caused by too little or too much Desired Air Flow in Park/Neutral? Do I need larger or smaller numbers in the table cells for Park/Neutral?

[WeathermanShawn]

That would be my guess.

If it stays at a higher Idle, obviously there is too much air. Does it decay within a few seconds or just hang there?

If it decays fast then it could be of the Start-Up Airflow Corrections..most likely Start-Up Friction Airflow Correction. If it just hangs I would try lowering your Park/Neutral Airflows in .5 g/s increments. Iit should become obvious pretty quick. Again, this is assuming you are totally stopped and at Idle..

[blsnelling]

Yes, completely stopped and at idle. It stays there and never comes down. It also continues to fluctuate.

[WeathermanShawn]

I am assuming B4310 has all zero's (it should). B4315 should also be zero at 0.0 TPS.

No doubt it is an Airflow Parked Table. Anytime your RPM's are at or below desired Idle value, thats where all your Learning Airflow Parameters B4512-B4516 kick in. So, it is somewhat 'normal' for Rpms to fluctuate in that case.

I would attempt to lower your Desired Airflow (P/N).

[blsnelling]

I am assuming B4310 has all zero's (it should). B4315 should also be zero at 0.0 TPS.

No doubt it is an Airflow Parked Table. Anytime your RPM's are at or below desired Idle value, thats where all your Learning Airflow Parameters B4512-B4516 kick in. So, it is somewhat 'normal' for Rpms to fluctuate in that case.

I would attempt to lower your Desired Airflow (P/N).

B4310 is all zeros, but B4315 is 1.00, the factory setting. So change it to 0.00 ehh? Did I miss that in the tutorials some where? Don't remember seeing it mentioned.

Can you explain why idle trims don't bring the idle down in a case like this?

[WeathermanShawn]

B4310 is all zeros, but B4315 is 1.00, the factory setting. So change it to 0.00 ehh? Did I miss that in the tutorials some where? Don't remember seeing it mentioned.

I have included my TF Airflow via attachment. Normally, you don't want it active at 0.0 TPS. Mine is stock.

Can you explain why idle trims don't bring the idle down in a case like this?

It is probably too much of an Airflow Correction to be learned (hard limits). You really don't want large corrective airflows to be learned, or your Idle would swing wildly all the time.

This is my best 'guess' as to what is happening. Remember all the TC,TF Airflows need to eventually decay or Idle will hang..Give those a try..

[blsnelling]

My bad Shawn. I was looking at B4321 My B4315 ranges from 0.00 to 0.13. That's still a huge difference from yours.

[WeathermanShawn]

My bad Shawn. I was looking at B4321 My B4315 ranges from 0.00 to 0.13. That's still a huge difference from yours.

I'm not sure if there is a M6 vs Auto difference on B4315. A B4321 of 1.00 is exactly what you want.

Nevertheless, its probably still your Airflow P/N. Another 'fun' Pid to log is 'IAC SUM DMA'. Thats your total airflow. If you log it along with TC,TF, and every other IAC Pid your Scan Tool will allow, its easy to see how they all act as modifiers to the Airflow. Since SUM Airflow is the total sum..its a great Pid to help diagnose Hanging Idles..

[blsnelling]

Shawn, I've been going back through the Idle Tutorial and your idle tips. The main difference I see is that you don't recommend so much air in B4309, Throttle Cracker Airflow In Gear. He has his as high as 12.00, while yours maxes out at a little over 1. Comments? Here's my tune as of now. Should I lower B4309 back down?

My Modified_06 Big Idle Changes.tun

[WeathermanShawn]

The Throttle Cracker in Gear can be a tricky table to tune. A lot is personal preference, but you have to really understand the Table to tune it properly.

Too much air and when you let the foot off the gas, the car will coast forever. Since the additional air prevents the RPM's from dropping, a lot of times the car will begin to buck and or surge. Remember your foot is off the throttle, so injector flow is very minimum. Cam cars can really buck with a lot of TC Air.

Too little and when you let your foot off the throttle it will feel like someone just put the brakes on. It also makes the throttle feel stiff..like you have to continuously press it to keep at speed.

The 2002 LS1 M6 had a lot of TC Air in them. No other year did. None of the Automatics had that much air. I think SSpdDmon took out a lot of air in the lower Rpms and kept it at higher Rpms.

If you find your Rpms never drop at highway speed or you car overly bucks..take air out. I'm not sure an auto would want that much air in it. Personally I would start lower on the TC and try differing combinations. My car feels best with that 1-2 g/s in the TC. I put most of my air in the Throttle Follower. That way you get the air when you push the throttle down, but when you let off the throttle it decays almost instantly. Its kinda like an old fashion 'accelerator' pump.

Sorry for the dissertation, but thats my best take on it.