Return to idle issue....

[Redline Motorsports]

Been busy lately with cam installs with the E38. I am trying to resolve a funny issue when the rpms return back to idle from deceleration. Idle drops right to the desired rpm and then raises a couple hundred rpms for a about 2 seconds before returning back to the desired idle rpm. The car never stalls and returns down to the desired idle rpm very cleanly. Picture pulling into a parking lot and pushing in the clutch as you roll to a stop. The idle drops to 875 and then jumps to 1000 for a short time before coming back down to the 875. Been seeing this alot after cam installs. Tried reducing minimum airflow and its doesn't appear to be timing related thus far.

How does the PCM know what gear you are in with a manual trans when looking at the minimum air table?

Howard

[ntae]

I have been trying to work out what pid to log for manual trans to work out the gears for a while with no success . i was thinking of making a map like we did with the older pcm's , i even got out my dark side cable with no luck . i think ross said the clutch E38 tables should be in the next update

i have notice the rise in idle more after refitting the maf

[Redline Motorsports]

I am not aware of any sensor on the trans that outputs individual gears in a manual so it would be real interesting to see how that get that axis data.

I am still not convinced that this table is the place to deal with this as I have tried a number of different air combinations with no luck.

[Ben Diss]

Howard- Is the idle coastdown spark table and base idle spark table close in your final idle area? I'm chasing this down too, and I think this may be cause. I see 10-13 degrees advance during coastdown and the idle is reached right away. Once I come to a complete stop, the idle bounces up and a few seconds later settles down.

[Redline Motorsports]

I need to pull the file and check. I usually like to get them close to ease the transition.

[jfpilla]

Howard,
The e38 does not use a TCracker table. Does that mean spark is the replacement? If so Ben may be right. Add timing to coastdown and it might slow rpm reduction. Too fast rpm reduction is one reason for rpm bounce.
Joe

[Ben Diss]

Another thing to consider is that the Final Idle Airflow might be too high. I had this symptom and solved it by reducing mine. I must have made a mistake when I calc'd it. I have a moderate cam, and a good idle at 750. I had 9.21 as the final idle air, but when I brought it down to 8.15 after doing the calc again it solved this. I can't explain why, but that's what worked.

In my logs I had noticed that the TPS under good idle was 17, but during the bounce up and subsequent delay it hung at 20 then slowly went down.

Good luck.

-Ben

[hymey]

I just put a cam in my car today. It does the same as yours Howard and I believe it may be related to coast down spark aswell.

With my factory settings the min. airflow ECT multiplier is set at 0.5 cold and gradually reduces to 0.25 at running temp. I have my min idle airflow set at 10.0 with a 226/232 114 cam on 114ICL. So realistically at running temp min idle airflow is 0.25 x 10 which is 2.5. If its to low, like 8.5 it hunts at idle, I step it up until its starts to hang a little like start at 10.5, then go back 0.25 at a time until it settles at desired idle rpm. I have mine idling at 800rpm I set 10.0 at 800 rpm, then 10.25 at 600, 10.5 at 400 and so on, same goes for higher rpm, I step it up .2 at a time. That way once the min. idle airflow is set correctly it will sit in place without hunting.

If it still hangs a little, like your issue, I found with MAF tuning after a week or so of generally driving the pcm learns idle and it behaves better, The ETC has some learning going on we can't control. Hope this is of some value to you. There isn't much info on idle tuning for e38.

Cheers

Joel

[hymey]

I was able to get the car idling very well at 800rpm with a 226 232 114 cam. I tuned the VVE in mafless first and had the car running so well I was not going to reconnect the MAF. But after some testing, I found the car was running lean on gear changes like the E38 manuals in SD do. I disabled CFCO and it helped but not enough, It was slowing the car down, I kept increasing the fuel mass multiplier in stomp dynamic fueling, But it didn't work(dynamics doesnt work in SD it works on airflow). Reenabling the MAF sore a huge difference in afr from mafless at idle, I was at 15.5:1 way to lean. I made a auto ben map for scaling the MAF on the e38 using serial wideband and boy is this a god send. I did some autoben MAF tuning and I have never had my fueling so good and the car is very smooth and returns to idle with no hunting or hesitation. I then did some more WOT testing on a private track and the car does not go lean on gears now. Also when I command a richer setting in dynamics it responds to it. So overall I am rapt. Getting it spot on mafless and then scaling the MAF to get fueling correct and very accurate everywhere. The response is awesome. If anyone would like a copy of the autoben map for MAF scaling and serial afr readings. Please send me a pm and give me your email address and I will send it to you.

Cheers

Joel