Help with oscillating idle on '07 LS7, big cam, heads, intake, headers, light clutch

[toy_collector]

I'm new to tuning and hope you guys can help me out. Finished this build five years ago. All was fine initially but after a while idle rpm began oscillating. Target rpm was around 950. Swings would go up to 1600 and then drop well below target. If it didn't catch itself the motor would die. Driveability was very poor. Lots of revs to take off. Lots of bucking under low rpm low load conditions. I had a few tuners "fix" it but the problem never really went away. I've avoided driving the car for last 3 years but its time to fix. Note the car runs great under throttle (700hp+ at the crank) but will lug heavily below 1800 or so. Wasn't a problem when I was doing track events, but I'd like to get some street driveability. Cam is 241/251, 650/658, 112 +2.

I studied the existing tune (as provided by the build shop along with changes made by other tuners) and noticed the idle effective area was set at ~8175. The math works (kind of) for a NW 102 tb, which I was running, but went back to the 90mm stock size to rule out the tb as the problem. Oddly, in looking at stock tunes for a '07 Z06, they all use ~8175. Why? In any event, I searched this forum and found others using ~5600 for a 90mm tb so that's what I changed to.

I started the car and it started oscillating again. I let it go a bit and in the course of hunting down a port to plug in a manual vacuum gauge, found that when I pulled off one of the intake hoses, the car ran a lot better. At least for 20 seconds or so. Which I figured to be the ecu learning according to the parameters. Seems more air is needed so I updated the tune with ~15% more base running airflow and restarted. Much better. A brief little test run around the hood shows the car will still buck if light on the throttle and under 1800 rpm. Going up a gear or two forces more manual throttle input which smooths it out.

I pulled the attached log. I'm clearly not an expert but it seems the O2s are swinging quite a bit. Anything jump out at anyone?

Fuel is fresh. Cats are clear. Plugs are new AC-delco iridiums. Smoke test showed no intake system leaks.

Note that during my test run there was a brief hesitation under throttle stab.

[schpenxel]

Have you gone through the idle tuning thread that BigMike made? It may be a few pages back in the forum now but try to find that

Also would help if you had a wideband, I assume you don't? Narrowband O2's are always going to switch back and forth in closed loop

[toy_collector]

I didn't previously find BigMike's idle post but I'll look again. I did rely heavily on Rinkrat456's idle tuning post in the gen3 forum to make sure I was at least in the ballpark.

Ok, you busted me. I do have a wideband. Car is already on the stacker, just need to wait for a good weather Chicago weekend to pull out the car sitting underneath.

[rao]

Come on, the weather is fine

In this sort of situation I would put all idle-related settings back to stock and start from scratch. BigMike's write up is an excellent place to start.

[toy_collector]

Took a few months to get back on this tune issue, but finally have time. Added in my Ballinger AFR500 WB O2 sensor and generated the following. As a side note, the car idles MUCH better than before but when driving if I stomp the throttle the car takes off a bit slower than before. E.g. it's not the madness of acceleration that used to be there. Not a totally bad trade-off since I can actually drive the car in traffic now. Any tips on tweaking the tune are greatly appreciated.

Thanks all!

17-05-29 12-43-52.hpl
layout1.Gauges.xml

[5FDP]

Based on just that log and no recent tune to look at you'll need to adjust your VVE and MAF curve.

The fuel trims are pretty much +10 for most of the log file showing you that more airflow table adjustments are required.