Beginner here having a strange hunting idle in SD while trying to tune VVE. The car is an L92/LS3 swap.
Only happens when the engine comes up to temp, idling in neutral (car is a 5 speed manual) at stoplights etc. Car seems to run fine otherwise. Problem was not present when tuning MAF.
When it happens, log shows steady timing bounce between around 6-20 degrees and AF between 1.0-1.14
Tried adding to the idle zone in ve table, bumping up rpm, base air, idle timing 15 degrees with no luck. Problem either got worse or went to bouncing rich to lean.
Hoping someone can take a look at the attached recent log and tune file and hopefully provide some insight. The first instance of the issue happens between 0:10-0:18 standing at a light. Looks like a perfect saw tooth pattern across the chart.
Leva, you may want to start by matching the Start up Idle more closely to the target idle. You are asking for 700 rpm on a warm engine but your start up grid is 650. {[ECM] 33601 - Startup Idle Speed PN} and In Gear. Modify both grids.
In looking at your scan the O2 sensor voltage is fluctuating causing the timing to sea saw. Bank 1 sensor 1 is constantly low.
My thoughts anyway!
Last edited by Robert C Morgillo; 12-08-2020 at 06:19 PM.
Thanks for the reply Robert. The idle differences are one of the adjustments i forgot revert back, playing with the tables. I will def change that back.
Regarding the O2's, Im running in closed loop with everything failed, trying to dial in vve with wideband and eq error. Dont believe the O2's would affect my timing. Maybe Im wrong? Still learning
Your front O2 sensors are always running the show. Without them working properly the fueling will be wrong and a few other things. The timing is one thing the computer is using to try to control the engine speed. If you look at the scan graph lines while the engine is idling, you can see the O2 voltage green line and the timing white line both sea sawing rapidly. Those should be steadier. The EQ error is over 25%. Is that correct? I am thinking you need to check the O2 sensors. Do you have headers?
Last edited by Robert C Morgillo; 12-08-2020 at 07:49 PM.
Robert, the eq error sea saws between around 4% and 14% when the problem happens. Otherwise fueling is normal as i am getting the ve dialed in. Im within around 3%.
I do have shorty headers.
When i go back to closed loop, the 02s and trims look to be functioning as they should, and sea saw idle is no longer present. In Maf only tune, the does not exist either.
Leva, that is really odd the way the timing and consequently the O2 voltage is sea sawing. I took a hard look at your tune and the only thing I could see is you may want to turn off the [ECM] 270 - Manual Trans Spark Smoothing (RDSC) Master Enable and Zero the VCP Spark: Spark modification based on Variable Cam for the SD tune. Something is definitely yanking the timing up and down. At 30kpa and 650 to 800 RPM your commanded is around 22 deg. You are getting 4 to 25 deg during the "sea saw". Your IAT is trying to pull 3 to 6 degrees as the intake air warms to about 60 degrees. The intake air is changing quite a bit as you are driving. It might be the IAT table or the spark smoothing. I looked at some of my SD tune runs. Nothing shows that at idle. I always 0 the IAT and disable smoothing however. Who knows, keep trying! There are some extreme Pro's on here. One of them will get you through!
Take a look at ECM] 12621 - IAT Spark Advance Correction. When I look at your scan you are idling in the area where it is adding Neg timing. That only accounts for a few degrees of the timing retard however. Something else is pulling a lot more timing somewhere. I will keep looking. Someone who is good at this might spot it for you. You might want to look at this table also [ECM] 12612 - Idle Base Spark.
I played with the idle base spark table initially when the problem first appeared with no luck. I will def play with the IAT table next. Seems very relatable to my problem.
The flattening you see in the scan is when the idle corrects itself. The problem is not consistent if the car idles for a while. It will go back and forth between the seasaw effect to a steady idle without the timing pull running lean, hence the low and flat 02 voltage. A loose connection also crossed my mind, so today i checked O2's, grounds etc. Connections seem ok
Interesting thing I noticed today with the hood open, the idle stabilized exactly when my electric fan kicked on. Not sure there is a correlation, as the problem shows up at a broad range of temps, both iat and engine. But the one constant is the engine needs to be warm for the issue to start. Also, the fans operate independent of the ecm, through the cars stock relays and radiator thermoswitch.
Your Idle Base Spark should more closely match your main spark table. I have heard that if your timing tables don't somewhat match, it can cause the corrections to fluctuate. I always try to make them match up.
Robert, just want to thank you for all your time/input.
Seems I fixed the problem, at least in the interm. The issue is definitely related to iat like you mentioned initially. I have concluded its due to heat soak in the engine compartment, as my iat temps can hit 160 degrees idling. I added 3% air to my idle zone in the VE table, and that has cured the seasaw. But still running super lean as the iat builds up. All makes sense since i am in open loop and trims are not there to clean up. Need to rebuild my intake and relocate my maf/iat.
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