PCM Diagnostics & Tuning - Engine stalling going from speed to idle
04-15-2012, 07:21 PM
What HP Tuners tables dictate how the engine comes down to idle from higher RPM?
So far I have the idle very close to perfect however when I idle down it tends to drop to 300 RPM and it will stall 40% of the time, the other 60% it will recover into a normal Idle. This happens when decelerating as well as revving the engine at a stand still (car is a M6).
The VE table is nearly dialed in as well so it is not a fueling issue, also I have adjusted the throttle follower table with no luck.
Thanks for any help as this is keeping me from driving the car more, since I'm paranoid about stranding myself by killing the battery or starter from all the restarts I'm having to do.
Car is 2002 TA M6 LS1 stock cubes.
There isn't just one table. It's likely idle air and spark. There are lengthy and informative discussions on the HPT forum regarding idle tuning. Stock cubes isn't really the issue. The issue is cam, intake, TB, etc.
You'll find everything you need over there.
04-15-2012, 09:40 PM
I found my MAF being off the main cause for that very issue for me. Try to follow the tuning guide first to get yourself dialed in then see how it behaves once it is.
04-16-2012, 08:27 PM
The car does not run a MAF as it's failed out on purpose (I do not want to re-enable it). I have been on HP Tuners board doing searches for days and no one really covers it fully, this site also sees more traffic then the HP Tuners forum. I understand the changes are due to the changes I have made and not the cubes, was just letting people know it's not a 427 or anything.
04-17-2012, 09:48 AM
I've been trying to track down an open loop issue on my car. My closed loop is near perfect and doesn't have the same issues as yours.
From my understanding of the change to idle mode from revving, cammed cars have a more difficult time when the idle is more rich than lean. It's in the transition where all of a sudden the air supply is cut and the IAC has to adjust to get more air in, but there is a flood of fuel from the air being cut from the throttle blade being snapped shut.
I was playing with my MAF settings and found that it was physically dirty so the settings were rich by 6-9 percent in the low frequency range. When adjusted to +-1.2% I found that when on the lean side, the open loop drop to idle from small revs and the car moving <2mph was not stalling for me.
If you are stalling out on SD and you've been messing with the VE, how can you say for certain that your VE at idle is perfect? Post your tune and logs of the events to see what is occurring during those times while in closed loop.
04-17-2012, 11:40 AM
My fueling should be close by what my wideband is telling me but I'm going to revisit it later today when I get home as well as my Idle airflow tables with my STIFT turned off to be sure. It probably needs looked at since I've made changes trying to nail this down. I'll refine it and post up a log, tune, and config later today when I'm finished.
04-17-2012, 08:01 PM
OK just back in from some new tune changes and a new log. I went back and revisited my RAF table to be sure and also to decrease the throttle follower decay. It seems to have helped a little bit but I'm still having issues as seen on the back half of the log.
I was wondering if my high MAP low RPM VE fueling is needing some work. I noticed that my AFR error in that section says it needs more fuel but I'm not sure since I didn't log those cells a whole lot.
Feel like I'm getting closer to the answer but I'm still a ways off.
(the Idle-Airflow.hpt file is my config file so just replace ".hpt" with ".cfg" after you download it)
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