Intermittent Stalling...

[ArKay99]

My mods are in my sig. I also installed a 2002 Z06 OS and am tuning with that. All in all the car runs great but here is the problem and I've been at my wits end trying to find the answer. I only know the symptoms.
When I start the car and let it idle, it idles perfect. I back it out of the driveway and drive to the corner, about 100ft. It's perfect. I drive normally and go through the gears to 5th and cruise for about 1500ft in 4th or 5th at 30 to 35mph and sometimes, not always if I take my foot off the accelerator and push the clutch in, like I'm rolling to a stop, the engine just dies. I have tried all sorts of combos. Adding lots of air to the throttle cracker, adding and subtracting small amounts of air to the throttle cracker, taking out air from throttle cracker all together, adding and subtracting air from the throttle follower. I have set my DAF to RAFIG, RAFIG is within +-.1 most of the time. The LTFT's are within +1 -> -4 and if I could get the car to stay running I bet they would settle to within -1 to -4.
I have done about 100 idle transition tuning logs and they are different, but not by much < .300g/s overall. There are no intake or exhaust leaks I can detect and the LTFT's track pretty evenly everywhere.
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What I have noticed is odd is this: The MAF and DYNAIR track very closely, i.e. they average close to the same, but the DESIAC_B is VERY low in comparison. If I enter the MAF values into the DAF table my RAFIG map is -3 to -4 gs/sec everywhere, and the car has a hard time idleing and won't stay lit at all when driving down the street provided I can get it going. If I use the RAFIG values they get very close and the car is very driveable except for the intermittent stalling. The intermittent stall exhibits thes symptoms. When I'm driving along at 30-35mph in 4th or 5th gear, 1200-1400rpm's, the car will go from a state where it is going along very smoothly to a state where it starts bucking against the gearing, almost like I am turning the iginition on and off rapidly. No power for approx 300ms then power, then again, and again, it's not rhythmic, but random. You can feel it and hear the engine banging against the gearing, but it's not violent. I don't detect misfires when this is happening, and my WB02 says that AFR is right at 14.6. If I take my foot off the accelerator and push the clutch in at this time then engine will stall, much like the tb blade is slapping completely shut. If I am going along and don't have the above noted symptoms, and roll to a stop, the car behaves just like stock. One other thing I have noticed when the bad stuff is happening is the idle trims and ultimately RAFIG show LARGE differences from the parked and logged values, like 1.55gs/sec, or -145gs/sec. Also, it's worse with AC on than with off. Spark is normal, although I had bumped it a few degrees in the idle area, and there is no knock retard detected.
What am I missing? Sorry for the long post. I just wanted to give as much detail as possible.

[ringram]

Hmm, did you start at stage 1 and tune it nice with SD? If not Id do that.
It could be various things. Someone else might have some more specific ideas. But does it also happen in SD mode or with and without maf?

Let us know how you got to the tune you are now running. With that cam you would really need to go into sd mode tune your ve and get your idle and raf sorted out before moving on.

Your maf and o2's might be hiding some fundamental issues with your tune baseline.

[ArKay99]

Doh! With all the detail I provided I forgot to tell how I have the tune I'm running now. I did put the PCM into SD using the Auto Tune tutorial posted in the Please Read Here First forum. All went well and I have a nice smooth VE table. I also cal'ed the MAF using a BEN table I found on here and AFR is very close with it, and the numbers didn't change a lot. One thing I did notice as I was tuning was when I had my IFR table scaled for the 30lb/hr SVO's the VE values were up around 130-140! So I scaled the IFR table back by a coresponding amount so my max VE values were within 100.
I'm not sure why this occured, but my injector duty cycle is around 85%-90% and AFR is 13.2 at WOT with the WB on the street everywhere. I am thinking of putting in a new fuel filter, mine has 34k miles on it, but there are no indications, at least from the above, that fuel is choking.
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One point you brought up that is well taken is SD mode and MAF. I think I may put it back to SD mode to check that the MAF is working correctly.

[ArKay99]

Ok, I put the car into SD mode and went to square 1. Started up fine and idle settled in fine, except AFR at idle was between 12.5 and 12.8. All other cells in the area were actuall a little lean. 15.2 15.7 I did a short idle log after fully warmed and applied the BEN factors to the VE table and after few iterations the idle is now 14.6-14.7. Also, I used to have a LOT of idle correction in the form of adding disproportionate values for the Idel learning tables. Low values in the Drive high columns and extremely high values in the drive low columns, mostly in the Direct AirFlow tables to keep the engine from stalling if I blipped the throttle for example. I now have stock values in those tables and although they are a bit 'soft' the motor now recovers if it goes lower than idle on a blip or sustained off idle throttle. I am going to finisha thorough VE table auto tune and get the values right at 14.6 everywhere especially at idle before I continue on.
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I will update as I go since I believe I have been dealing with a miscalibrated VE table from the beginning and this has made it impossible to tune.

[TAQuickness]

Did you try adjusting the TF decay rate? I found when coming to a stop from low speeds, I needed a little longer TF decay to make the transition.

Edit:

Different topic, but if you ever have to make a new top shell gasket for your fast90, get a 5cc seringe (sp) from your local pharmacy. Makes it a lot easier to get a consistant bead with less mess.

[ArKay99]

Did you try adjusting the TF decay rate? I found when coming to a stop from low speeds, I needed a little longer TF decay to make the transition.

Edit:

Different topic, but if you ever have to make a new top shell gasket for your fast90, get a 5cc seringe (sp) from your local pharmacy. Makes it a lot easier to get a consistant bead with less mess.

Yes, I think I can write a book on all the little adjustments I made to TF, TC, all the idle learning tables, and timing enablers too. I've learned quite a bit about all those tables and how they interact in dealing with this 'current' issue. I think the bottom line here is, yes I will need to tweak the TF and TC for good transitions, but having my base cal out was causing other problems in the tune that I had 'tune out' using brute force. For example in the Direct Airflow Correction table I had to increase the the value of the RPM Low Drive and Rpm Low Drive A/C by 1000%, yes times 10, and lower the the PRM high drive by 600%, in addition to changing the associated control delays by -50%. This made my transitions rock solid when standing still, but gave me the intermittent problem I was having as spelled out above. I am by no means saying this has cured my problems, but by getting my fueling in line by realigning my VE table has produced the same effect using stock values for those tables. This says to me I was compensating for the tune.
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Did you do the top shell gasket using silicon? Since I posted that I removed my 'homemade' gasket and got a new topshell gasket and a set of new FAST port gaskets. The port gaskets are about .080" thicker than the stock ones and the new topshell gasket fit in nicely. It's actually a 'rope' of whatever gasket material they use. You have to cut it to size and use a dab of silicon where the runner gaskets meet the perimiter gaskets. I did this because I didn't know if I had a good seal at the time and I've been working on this problem for a while. I may go back to a 'homemade' gasket, but for now this seems to have worked.

[DaddySS]

Ok, I put the car into SD mode and went to square 1. Started up fine and idle settled in fine, except AFR at idle was between 12.5 and 12.8. All other cells in the area were actuall a little lean. 15.2 15.7 I did a short idle log after fully warmed and applied the BEN factors to the VE table and after few iterations the idle is now 14.6-14.7. Also, I used to have a LOT of idle correction in the form of adding disproportionate values for the Idel learning tables. Low values in the Drive high columns and extremely high values in the drive low columns, mostly in the Direct AirFlow tables to keep the engine from stalling if I blipped the throttle for example. I now have stock values in those tables and although they are a bit 'soft' the motor now recovers if it goes lower than idle on a blip or sustained off idle throttle. I am going to finisha thorough VE table auto tune and get the values right at 14.6 everywhere especially at idle before I continue on.
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I will update as I go since I believe I have been dealing with a miscalibrated VE table from the beginning and this has made it impossible to tune.

Found this thread doing search because I have the same near stall/stall situation. Did you get it fully resolved through the action you describe?

Also noticed you are right down the road from me!

[ArKay99]

Yes, I did. Then I dropped a very thick and strong washer into my #7 cylinder while chasing a vacuum leak, didn't notice it, started the engine, and crushed the piston.
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There were 2 things I did.
1: One was to tweak the TF for throttle blip standing still. Same airflow amounts, I just changed the values between the 3% and 13% cells. Just added a bit more. This slowed the throttle blade a bit and kept it from dropping rpm's.
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2: The other and the hardest to find was the TC. I found it while logging AFTER I put some very large values into the airflow table at low rpm's and speed, and I put them in the 0 mph rows too. When I was coasting to a stop, with values about .5 g/s, I noticed the engine would surge a bit then settle. I then noticed that in the log, the TC airflow values were 0 while coasting to a stop and at some point, THE POINT WHERE MY ENGINE WOULD STUMBLE, I noticed the airflow values I had in those low cells that corresponded to the current rpm and speed, jumped up and started to die out according to the decay rate I had. So all I did was find a value that would keep the motor running at ~idle rpm's and put that into those cells, and it fixed that.
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I was having a lot of fun with the car but was chasing a vacuum leak when I killed it. Lingenfelter 403 on the way... Woodcliff Lake is a beautiful town, btw.

[DaddySS]

OK, thanks. I'll continue to chase.