I'm looking for some pointers to troubleshooting an odd condition, happens in open loop where if I try to drive it, ie back out of driveway, it will stumble and struggle to find idle. If I drive it for a bit, as soon as I hit a stop it will struggle with idle. Restarts are rough and require some throttle playing. I've got nothing in sensor readings really for this time since I have to wait for the car to cool down significantly to reproduce and even then, its not 100% guaranteed it will re-occur. Once I hit closed loop, all is well. So I've got the option of wait 2 min for car to warm up to closed loop from cold start or try to fix tune.

I've been toying with the idea in my head that my "cold air" intake has messed up my idle adjustments in the VE but I've tried to ensure datalogging once the IAT are normal and I'm on the road for it not allowing heat soak during logs.

I uploaded the cfg I was using to monitor everything along with 2 logs of after I dialed in my street tune portion for both the SD and MAF. I spent a good few hours of tweaking the SD portion over various days and finally getting the MAF to match.

running
L92 6.2L
5.3 heads stage 2.5 65cc
LS6 intake
0.615/0.608 lift 230/230 115+2
m6 emissions equipment intact

I can only log 24bits so I had to delete the O2 readings for bank 2 when logging.

I was also going thru the tune and found some oddities that the tuner had done to my car, in Engine, Fuel Control, OL & CL and found anomalies vs a stock 98 tune in which the areas relating to open loop may be the issue. The open loop EQ ratio is lessened for all areas 122 F and less and 55 and less. This would be the area that stumbles in open loop for me but am not sure if I should bring back to stock, increase or further decrease.

Any thoughts and suggestions much appreciated!

 

Update:

On moving from a parking lot I was able to induce the condition by moving the car down a ramp, I was out of gear and coasting and as I went down the ramp (long parking garage) within maybe 3-4 seconds the idle started struggling as the mph picked up. It seems to me that while in open loop if I start moving a new factor comes into effect. Could this be the throttle cracker?

 

A lot of the airflow tables are VSS dependent ...

Look at throttle cracker. Sounds like he dialed in enough air while at stopped idle but not rolling.

What are your IAC counts, parked and rolling?

 

I'm going to try to replicate the conditions in a bit and do some logging, just letting the car cool right now. Hoping I can get it to happen and see how it shows up in the logs.

 

So I did some start ups playing with a few things and no change. I did a log of the IAC count at startup and found that on this particular attempt to start after a new flash and fuel trims cleared I had a "stumble" when I tried leaning out the VE tables related to idle, I guess I'll put them back to the above tune but here's a log of my IAC count in closed loop.

When it stumbled it brought the IAC count to 180s after it settled it was 125 avg.

I reset to my "base tune" in the first post and did another cold start just after flashing.

I found that my iac counts are around 114 on average. I still had the wild drop off at the start, not sure where that came from, but its not as bad on subsequent starts or when warm its almost gone.

-update: cleaned MAF, had a good film of carbon on it. Re-tuned MAF was off by 6-9 percent down low and 3-5 as it climbed the table. The "stumble" start has been reduced and its seeming like its a little lean at idle giving off a slight "burn" your eyes feel. I'll see how it is in the morning when I go to work after it sits overnight and gets really cooled down.

I'm going to try the "set screw" method of opening my throttle 2% and recalibrating the TPS then play with the throttle cracker over the week and see how it goes.

 

I think I need to play with the open loop idle characteristics. I was inside waiting for something to finish and was listening to my exhaust note on my car this morning. It sounded like a decent sized cam, good lope, almost harley like. Then it hit closed loop and it sounded so tame! Smooth LS1-like style exhaust note.

Also when I backed it out, while it didn't die, it did stumble. It happened as soon as I revved it and it was rolling out of the drive way near the bottom. For the first 20 ft it was normal idle until I hit the point where I gave it some throttle then it stumbled, but it recovered. I initially gave it some thottle thinking it would stall, but it was recovering fine on its own.

I'm going to read up and work on the open loop portion, but any input based on the above tune would be welcome.