Questions about surging, intermittent idle hang.

[LinearX]

I'll get the engine out of the way first.

Stock bottom end, stock cubic inch LS6
AFR 225 @ 60cc
240/244 .598/.605 112+4
Ported FAST92/95mm throttle body
Kooks 1.875" headers, x-pipe

I did all of the driveability tuning on the car from CPIG's guide I found here. I checked AFR with an LM1 wideband.

A friend of mine did the WOT on his Mustang Dyno, again, using the Mustang supplied LM1 as AFR reference.

The car surges when idling through a parking lot. I'm not sure if it's related to timing or if I just have to live with that to some degree due to the nature of the cam.

The car also wants to idle hang from time to time. It generally happens when I go from using the AC to not using the AC. This morning when I drove to work, without the AC, it was hanging at right about 1500 (I forgot to log it). At lunch, it wasn't hanging, but the idle started to hunt a bit which is something it's never done much of. I turned off the AC before coming to the next stop and it was not hunting. I was hoping to catch it hunting in the log on the way back from lunch, but by that time it had learned it's way out of that mode.

I've done both Russ K's idle config and EC_Tune's idle config for RAF. When I plug the numbers into the RAF table, the car will start and idle fine, but it will die as soon as I push the clutch in when coming to a stop.

Here are the logs that I have from today, the tune that is in the car, and the log from when I did the RAF log with EC_Tune's idle config.

Note about the idle config log. I did this back in April when it had gotten really cool one night, probably down into the high 30s. The car was in the garage, I pushed it out, disabled the fans via the VCM control and started the car.

I'm open to suggestions on things to try to correct the intermittent hanging idle that seems to follow my use of the air conditioning, and if there is something that can be done to ease the low load, low rpm surging.

Sorry for the long winded post, I just wanted to make sure that I was including everything. Of course, I'm sure there is something I've missed so chime in if I've missed something obvious.

[LinearX]

Bump.

No opinions?

[LinearX]

EC_Tune, Russ, or any of you other idle geniuses feel free to chime in and tell me where I need to look first.

[WS6FirebirdTA00]

You are surging because the AFR is quite lean. You may get some, but a little more fuel may help out. Your throttle cracker table is also pretty high, that may be causing the idle to hang. You may also want more idle timing and RPM. Is it a manual or auto?

[LinearX]

You are surging because the AFR is quite lean. You may get some, but a little more fuel may help out. Your throttle cracker table is also pretty high, that may be causing the idle to hang. You may also want more idle timing and RPM. Is it a manual or auto?

Sorry, forgot to mention that. It's a 2002 Z06, so manual trans.

I noticed on the surge log, that the timing is sweeping up and down pretty radically. The car idles like a champ at 950, and the idle timing is set for 22 degrees.

The AFR there is actually different than what the actual LM1 controller was showing. It's never read lean before in HPT, but it was that day for some reason. On the screen it was actually showing a bit rich, in the 14.3 range. I can verify that again. I suspect that either the LM1 has lost its mind on the analog output, I need to recalibrate the LM1 and the sensor, or I have a sensor going out.

I was thinking about zeroing out the throttle cracker table and seeing if that cured anything. Do you think that I should leave the throttle follower table alone? If I put the numbers from Russ or Doug's idle config in there, the car starts/idles fine but will die when coming to a stop. I would think that the throttle follower and/or cracker tables would need to be upped in that case. Unfortunately, I'm not sure which the best plan of attack is. If they will both achieve the same results, perhaps I'll try zeroing out the cracker table first...or at least lowering it.

[TXZ0603]

PLease keep this up to date. My car does almost EXACTLY the same thing as yours. I just installed a AEM wideband today and my afr is off the scale. over 18 at idle, surging, ect. Looking forward to see how you cure the problem.

[WS6FirebirdTA00]

Some surging may be expected with larger aftermarket cams. With fueling and airflow correct, you can tweak with the timing to see if you can find a sweet spot. Most issues I see with surging is too much idle airflow, too much follower or cracker airflow, or being too lean.

Surging at idle mostly has to do with timing and timing correction in most cases.

[LinearX]

Some surging may be expected with larger aftermarket cams. With fueling and airflow correct, you can tweak with the timing to see if you can find a sweet spot. Most issues I see with surging is too much idle airflow, too much follower or cracker airflow, or being too lean.

Surging at idle mostly has to do with timing and timing correction in most cases.

I don't know if you looked at my tune or the surge log I posted, but in that log the timing is up and down quite a bit. I'm not sure where that portion of the timing is controlled, since I've got the main spark table and the idle spark advance tables set to command the same amount of timing. I'm not sure where to look for that unless it's in the overspeed/underspeed table.

[WS6FirebirdTA00]

The only time you should have timing swings is at idle for the adaptive spark control. If it happens while you are driving, you need to make sure you are not switching between cells in the timing tables causing erratic behavior.

[LinearX]

The only time you should have timing swings is at idle for the adaptive spark control. If it happens while you are driving, you need to make sure you are not switching between cells in the timing tables causing erratic behavior.

That begs the question, is letting the car pull itself under it's own power considered idling or driving? That is where I think I'm confused as to which table to look in. If it's considered idling since there is no throttle input from me, then I would assume the adaptive tables.

If it's considered driving then I should look in the base timing tables. I'll have to check the log and see which cells it was in and whether or not it's switching between cells that have vastly different timing values.

[WS6FirebirdTA00]

if the speedometer is not zero (or some set value IIRC), it is not idling.

[LinearX]

if the speedometer is not zero (or some set value IIRC), it is not idling.

Cool. Then I'll look at the log and see what cells it's in and check that there isn't a vast difference in timing between the cells.

I hope to have a chance this weekend in work no the throttle cracker stuff and see if I can get the intermittent idle hang to stop.

Thanks for the input! I appreciate it!

[TXZ0603]

Any update on this?

[WS6FirebirdTA00]

you say your AFR is off the scale, can you not adjust it back down? or is this an intermittent issue?

[TXZ0603]

If you were referring me, at cold startup its around 12-13.5 after car warms up it shoots up to 16 and past 18. my gauge stops reading at 18 and shows ....... across it. I have HPT on order so it might be a few weeks befor I can get a scan. Will see if my friend is around so I could use his in the mean time.

[WS6FirebirdTA00]

got ya, sounds like it just need a good tune on it and you will be fine.