Hanging Idle with ETC

[Matt68]

I was working on some idle issues with an 01 vette today. We having trouble with the RPM's hanging when pushing in the clutch while moving. I tried adjusting the Throttle Cracker Airflow {B4309} taking the 1000 and 1600RPM rows to 0. I also adjusted the decay rate up to get it to drop down faster.

Sometimes it works great, and the car runs normally and other times it hangs. When it does hang, it stays at that RPM until I reach 1MPH. I changed the TC start/stop to 6/5, and it followed those speeds. I am not sure what else to change to get the RPM's to CONSISTENTLY drop down to idle. It seems worse after shutting the car off and restarting it. Once driven for a while it gets better. You can see in the logs that the TPS drops down when the RPM drops down, so I don't think that it is a timing issue.

Any ideas of parameters to log?

Here is an example of a log: coming off throttle - RPM hangs until speed is 0 (I thought is was at 5 while driving) then TPS and RPM come down.

C5_Idle_0011.tun
Idle_00012.efi


Thanks,
Matt

[Matt68]

Thanks for the reply Shawn.

For B4307, I logged the MAF vs. ECT from a cold start and plugged it into the Des airflow table. I thought it seemed high, and I double checked the units were correct on the logged vs. tune file and they look same-same. Could it be that my MAF needs tweeking at the lower RPM?


As for B4309 I was going off the tutorials using this as a stall saver. Makes sense though that it is interpolating and the minor changes I was making in the 1000 and 1600 changes were not making much impact.

http://forum.efilive.com/showthread....ht=idle+tuning

I know there is some learning that is done by the computer, but would it make sense that the hanging would be more prevalent right after start-up, and would get better as you drive around?

I appreciate your help,
Matt

[Matt68]

Normally if an Airflow Parameter gets 'better' as the car warms out, then it is pointing toward ECT as the controlling factor. That still pretty much leaves us with B4307. I was just estimating that from 80C+, your Airflow might drop another 1-2 g/s..just a thought.

That was one of the major changepoints when I started working on the idle. It was not having any "hanging idle" symptoms before this just a couple stalling/surging problems that we were trying to work out. Since I was assuming the B4307 was accurate with the log, I was trying to adjust the hanging with the throttle cracker tables. I will have to try and take some back out of there.

I am curious if B4321 is stock? Is that really supposed to be 6% TPS change?

It is not stock, I noticed that the lowest the TP% would ever get was in the 5's, so I took it to 6 thinking that it might not be dropping into the base spark map or maybe some other table it should be at with 1%TP. Maybe ETC doesn't use this since the TP is changed for the cracker function?

So normally I just advise one run a calibration comparison against stock. You never know what little function from start-up airflow to B4321 to IAC Effective area had been changed.

The idle parameters were pretty much stock when I started out. The car has heads/cam, and we did the ve tables etc and the car seemed to idle fine thoughout all of that so I wanted to leave the idle stuff alone. After driving around some there was some stalling, bucking, and light load surging bugs that needed worked out.

Thanks again, I'll have to do some more logging to see what I can find out. Hopefully I can post some positive results.

[Matt68]

From the description of B4321 - "If the throttle position is greater than or equal to this value, or increasing by more than this value (each 12.5ms), then the throttle follower airflow is added."

Sounds like it is either or from the description.

I took it as if my TP was over 1 (which it always was) then the TF was active.