I have been battling this issue in my truck now since the Z06 cam install and it's driving me up a wall. The tune is dead nailed down the way I want it, except when I'm slowing making a stop, the engine will go below IDLE stumble then come back up to idle speed. It does this with or without the AC on. But yet when I'm scanning, if I command the AFR to be 14.7 to 1 it comes back to an idle flawlessly like it should. So I guess my question is, what's the magic behind that button? When I click on it, what is going on in the PCM? This is what needs to be adjusted to get my idle to return to normal. Attached is a copy of my tune for those interested. Thanks for the input guys!

 

BTW the truck is a 5 speed truck

 

Is there any reason why your Throttle Cracker Airflow is zero'ed out? This is a 4.8 right? year?

 

wow, i've never seen anyone set the High RPM Disable that high before. You are 1bar right? I am not to sure that's a good idea in 1bar. You telling them pcm to use a combo of maf/ve until 8000rpm then use 100% maf.

 

You got me, this PCM is a nightmare. It came originally from Jesse at Wait4me, then Doug Rippie motorsports got their hands on it, then I've been trying to iron out all the issues on it since I got it back. I should probably just start over from stock and paste in my VE and Spark tables. Truck is a RCSB 2wd with 4.8L and 5 speed.

 

I was running in speed density only, but I want my 2 spark tables back and trying to resolve the dipping idle issue, so I re-enabled the MAF and have begun tuning again. I thought the MAF being disabled may have something to do with the idle.

 

2004 i take it. Your IFR is scaled. I'd copy a stock as you said and start from scratch man. Compared to a 2004 same file it's got enough difference to me that would hender idle/decel tuning. Versus' stock it has 98 differences and 396 simularities.

 

Yes it's an '04. Did some more tuning last night, enabled the MAF switchpoint to 4000 RPM's as suggested, copy and pasted the cells from a truck that had the throttle cracker enabled, and neither of those made much difference. I then got to checking the engine torque management tables and thought to myself, since the cam swap the engine has shifted the powerband up, since this is true, I copied the friction torque from a 5.3L truck and then since the 4.8L has a interia factor of zero (Why that is I dunno?) so I changed that to .1499 like a 5.3L would. Also copied all the air conditioning torque management information over from a 5.3L truck as well. Truck returns to idle much better and more consistently. Although yet it still does it ever so slightly. I then began picking through the idle airflow tab again and noticed that there was no difference in my RAF table vs. a stock one. I thought I had already tuned this once. I had only a few minutes before it was time to turn into bed so I copied and pasted the raf values from a 5.3L truck to mine and now it returns to idle TOO slowly. Meaning it likes to hang at 1000 RPM's then slowly come back to 600 over the course of 6 seconds or so. This must be where the problem is at. I will try to split the difference over lunch today (at work right now) between the 4.8L and 5.3L raf tables and go for some cruising. I think I'm on the right track now. Did I mention it's tough to tune in weather like this is today? 94 degree high today with dew points in the lower 70's. Thanks for your help dewmanshu. I'll post my findings.

 

When I did the Z06 cam in my truck, I had some issues with surging at idle at first like you described. I ended up increasing the required airflow at idle table and that fixed it

 

KB, how much do you recall increasing it? do you still have your Z06 tune by chance? I know 50% increase was too much so I am going to try a 30% increase over lunch. At least I'm going in the right direction. Now the idle hangs way high and comes down sooooo slowly. This means I just have to find somewhere in the middle