Idle Going Lean At Stoplights

[hartigan85]

Since the Cam install I have been tuning my car with HP tuners using the tuning school learn at home beginners course. I have the Maf tuned and VE disabled. I am having an issue at idle when sitting at stoplights. When i am sitting there in gear the car will idle just fine 14.7ish afrs then all of sudden the car will start to shake more and i can watch the afr gauge go lean to 16:1. But if i put the car into neutral it will go back to 14.7:1 normal idle no issues. It only happens when the car is in gear and at usually every time i am sitting at a stoplight for more then 7-10 seconds. I am going to go and get a scan in the morning, just wanted to see if anyone on here has any ideas first.

[G8 GT V8]

When tuning, did you tune your MAF at idle and in gear? Might just need to do that. How are your STFTs looking when this happens? They should be adding fuel to fix things...

How does your MAF curve look in that area? Sounds like you need to smooth things out a tad...

[djchubbs]

I would check or listen for vacuum leaks since you have the intake off.

[hartigan85]

Well i got a chance to do a scan its really weird, when it goes lean both my STFTs go to 0. But before and after the lean spot they are normal, going up and down. I have attached my tune and scan from this morning. I tried to attach my config file but it kept saying that it was an invalid file. If you can look at the scan it shows it happening at 2:11 and 5:44. I have no idea what could be going on.

Edit: Looked through the scan again and noticed that when the car goes lean my commanded AFR is 15.7 ish. What would make my commanded AFR change from anything other then 14.7 except when going WOT and PE takes over?

Hartigans G8 GT Overwrite test.hpt afr stumble.hpl

[STL_G8GT]

Mine does this... thought it was a side-effect of a cam...? Also, when this happens it will push against the brakes a bit...

[hartigan85]

Yep exactly what mine is doing. Feels like it is bucking forward and back right? Pretty sure there must be a way to fix it because it stops when i put the car in neutral at stoplights. The next time yours does it put it in neutral and see if it stops.

[08G8V8]

I get something similar as well. I have a NGK air/fuel sensor and have it wired to my Aeroforce gauge. It typically shows a 14.3/14.4 AFR at idle when at a stop light. It doesn't always do it, but after idling for awhile at a light, the AFR will climb up to 15.5/15.6 and sort of shake a little, it will stay there for 5-10 seconds, then it will correct itself back down below normal 14.3/14.4 range, then back up to the 14.3/14.4 range. The STFT's don't look out of whack during this. If it was a vacuum leak, it would be doing it more often and always around the same vacuum level at idle, but it doesn't.

Not sure what it is.

[STL_G8GT]

Yes, in neutral it stops doing it, I've messed with it in the past... I thinks its normal cam manners... why it does it sporadically, I don't know. My aem does the same.... (wideband)... jumps to 15/16...

[hartigan85]

I disabled the catalyst test in HP tuners under engine diagnostics and that has seemed to stop it so far. I will know for sure tomorrow morning when i go for a drive.

[norm8332]

I disabled the catalyst test in HP tuners under engine diagnostics and that has seemed to stop it so far. I will know for sure tomorrow morning when i go for a drive.

That's it I bet. It's what I was going to suggest. But a side effect of messing with some cat settings could be fried cats - not sure about that setting though.