Idle Issue

[LS1guy]

hi, i have an ls2 with heads and cam and runs great. It has been tuned by many different people and the idleing problem was never able to be fixed for some reason.

The prblem is that when i start my car in the morning the idle jumps from about 400rpm to 1200 rpm but it eventually stables out (but sometimes stalls).

But if i come to a short stop in my car it will do the same thng and it usually stalls. I have the same problem when i put it in reverse going to my driveway the rpms are going up and down up and down. Same thing sometimes if i brake to go around a turn the rpms start doing that again.

But when it does idle normal it sounds really healthy and it runs perfect.

is there any advice that i can give to my tuner so he can fix this problem once and for all.!!

thank you

[MNR-0]

You need to log the car under all conditions when it does this. You need to big picture of what is happening and then address the symptoms one at a time.

Attached is my idle config. Use it when logging, along with the Default config for TRIMS and injector pulsewidth.

What I have done in the past is this, in no particular order:

Get standing idle STIT and LTITs in line, cold start to warm.
Set Base Idle Advance to 22*, using the Main spark table to work from
Raise timing in main advance tables in 0, 400 RPM cells to assist isle control during transitions from moving
Run in open-loop up till 1200RPM
Make sure your cracker and follower airflow adders are 0 when coming to a stop. If they arent, you will have have no idle control until they do. You can only monitor this using the scanner
Reduce the ECT fuel adder after startup in the main fuel section by 0.06 across the board
Reduce the idle overspeed/underspeed adaptive idle correction values by half up till +/-100RPM, blend in the rest
Set Idle RPM to 900 in Park, 870 in drive (for 228+ cams)

Your tuner needs to have a logical approach to all this. Just don't make changes without thinking about them or you will be shooting in the dark. Always use the scanner to monitor changes.

Finally, if you are using a MAF, its easier to achieve steady idle transitions going MAFless. MAF still works, but its just a little more fiddly and time consuming due to airflow being monitored dynamically, as opposed to pre-determined.

[98A4LS1]

After logging idle desired airflow, for each temperature, do you plug in the max value seen or the average or the lowest?
After logging (P/N cold startup), the data indicates I need to lower the BaseRAF at certain temps, however, it makes the idle hunting worse. If I increase the the BaseRAF values, the idle (cold start) improves.

[LS1guy]

Thank you guys. i will let my tuner know about all this first thing monday morning. THANKS!

[MNR-0]

After logging idle desired airflow, for each temperature, do you plug in the max value seen or the average or the lowest?
After logging (P/N cold startup), the data indicates I need to lower the BaseRAF at certain temps, however, it makes the idle hunting worse. If I increase the the BaseRAF values, the idle (cold start) improves.

For cold starts, I dont simply go off the average airflow values logged in the scanner, at least until its running at stoich AFR, which is around 1-2 mins after startup. This is because the car adds ariflow PIDS like startup idle airflow, fricton airflow and one which I have never been able to find in the editor, idle startup retard airflow. These adders need to be subtracted from the average results to derive the base running airflow for cold starts, and for the first 10*C rise in running from stone cold.

If you dont factor these in, you could create cold start problems. My base running airflow is 32+ when cold, ramping down sharply to 26*C arouns 15. Not that it matters much if your IAC counts are already maxed out at 310. But my cold start still rocks on fine.

[SSUte01]

If you dont factor these in, you could create cold start problems. My base running airflow is 32+ when cold, ramping down sharply to 26*C arouns 15. Not that it matters much if your IAC counts are already maxed out at 310. But my cold start still rocks on fine.

I don't have the spreadsheet handy I used to try an my model my RAF but I too have in excess of 32 and a steep descent (It seems to be a complicated exponential decay, I have a equation that works for my car enter the desired (read calculated hot RAF and it estimates the rest). This took me a significant amount of time to get right and ever since doing so my idle issues have disappeared, restarts are factory like and all but the coldest of cold starts are like stock. The coldest ones hesitate very slightly at about 800rpm prior to hanging at the usual rpm as it warms up. This is not bad and I can live with it. I always doubted myself that the figures were too high ie 32+ but it worked, so I stuck with it

[SUTTERERMAN85]

I don't have the spreadsheet handy I used to try an my model my RAF but I too have in excess of 32 and a steep descent (It seems to be a complicated exponential decay, I have a equation that works for my car enter the desired (read calculated hot RAF and it estimates the rest). This took me a significant amount of time to get right and ever since doing so my idle issues have disappeared, restarts are factory like and all but the coldest of cold starts are like stock. The coldest ones hesitate very slightly at about 800rpm prior to hanging at the usual rpm as it warms up. This is not bad and I can live with it. I always doubted myself that the figures were too high ie 32+ but it worked, so I stuck with it

i would be interested in this as well

[SSUte01]

i would be interested in this as well

Right-o at the risk of being lynched he are the numbers that I use. Please note that these are derived from calculated numbers at various temps and then modelled as closely as possible in a spreadsheet to help the numbers that are difficult to log. Let me just say that the model I used (exponential decay) may not be accurate for any car or even mine but these numbers work for me.

The extremely cold numbers are not based on the model but rather a linear increase and hand smoothed simply because the model being exponential produces extremely large figures that dont fit and more importantly I will never see colder than about 0*C (32*F) the model starts from 20*C up to max and less than that is a mixture and hand smoothed.

Also note that it doesn't consider all the factors that affect the airflow, ie cracker, follower, fans etc.

Anyways: From coldest to hottest (-40*C to 140*C) Car is 01 LS1 M6 H/C and average operating temp is 90*C (194*F)

50.00000 47.20996 44.41992 41.62988 38.48047 32.91992 23.08496 16.16504 12.13184 9.78223 8.41309 7.61426 7.14941 6.87891 6.72070 6.62891

It looks like a nice smooth decay, but if you have no dramas then dont change what you have that worked for me. So before its picked to pieces I stress this works for me and my setup

[LS1guy]

I never start my car at 0*c day and it is like 90 degrees every day and it still does it. once it warms up it idles fine. But if come to a short stop it will do it again. the rpms will start hunting and sometimes it has even pushed me through a stop sign or light. Its quite annoying. and if im at a show i cant even back out of a parking spot without the rpms hunting and stalling.

[30thta436]

FYI.

LS2's don't have any of the basic idle airflow tables like the LS1's. There is no throttle cracker, idle air flow, or follower, etc...

They have one table that incompasses the idle airflow and follower table. The best I can tell.

There is also no ltit or stits in the scanner for LS2's.