After Stop Idle Issue

[Dennis93TA]

Hey guys, need help with a idle problem in a 2004 GTO. It happens everytime you come to a stoplight about 15 seconds after you stop. The car will idle fine and the 15 seconds later it will stumble to about 300rpm and then struggle to pick back up and then idle at it's target rpm just fine. When it does this it only happens once per stop. It seems to me like the throttle follower but i didn't work on this tune so i really don't understand why some things are the way they are. Anyway can someone please take a look at the tune for me and maybe point me in the right direction.

Thanks,
-Dennis

[gto_in_nc]

This happens about 15 second after you come to a full stop? Is the Goat an A4 or M6? What has been done to the car?

[Dennis93TA]

it does it 15 sec after a complete stop, its an m6 it has an hpe c cam and stainless works full exhaust. It was dyno tuned by a guy in texas and it's done it ever since.

[gto_in_nc]

And it is fine after coming to a full stop for like 10 or 15 seconds before it stumbles?

[Dennis93TA]

yep. Ypu can watch the digital speedo and as long as you are rollin it won't do it. but as soon as it goes to 0 and about 10-15sec later it will stumble. I've never timed it or him either, but it seems to do it at the same time everytime.

[gto_in_nc]

My first thought is that it is related to the Base Spark table. The tune you posted has this table slightly modified from stock but I think not in a broad enough section. If you look at it, the previous tuner built a small plateau at low RPM & low MAP but, when I pull up one of my logs and link Scan to Tune (you didn't post a log), at idle I am resting along a knife-edge on that Base Spark table, not on the flat spot. What I suspect is happening is that, when you stop and it switches from Spark-High to Base, and things settle a bit, it falls off that ridge and spark advance drops suddenly. In my own tune (on an '04 GTO M6 with heads & miil cam), the flat spot on my Base is big enough to keep idle spark steady. (see my Base table below.)

http://forum.efilive.com/attachment.php?attachmentid=2224

BTW, it appears to me that the the car has no cats (stuff is all set to No MIL) but still has MAF, right? If so, you may want to look at the Spark Low-Octane Table. Looks like the previous tuner copied the High-Octane table to the Low and then left it that way.

[SSbaby]

it does it 15 sec after a complete stop, its an m6 it has an hpe c cam and stainless works full exhaust. It was dyno tuned by a guy in texas and it's done it ever since.

Mine used to do that too (cammed M6 Commodore). The only way I overcame the problem was to lean out and even out my VEs at rows 400 & 800 rpm. I didn't change spark tables. My hi-lo and base spark tables are identical at corresponding cells.

[gto_in_nc]

What do BENs look like, Dennis93TA? Softening the top edge of the Main VE Table as SSBaby is suggesting may be beneficial.

Do you have a log you can post? (Does the Goat have a wideband?)

[Dennis93TA]

No, i just helpin him out a little. I'm probably gonna start to try and re-tune some things for him. I was hoping it was something simple. I'm gonna have to pull my wb02 out of my car so it might be a little bit.

[gto_in_nc]

Take a look at the two suggestions in this thread first - they are both pretty simple. If everything else seems OK but this stumble, you might make him happy with a minor tweak.

Unless you just wanna tune his car! I happen to be rather fond of playing with an '04 GTO... :)

[Dennis93TA]

I'll see what i can do. Thanks for all the info.

[SSbaby]

I'll see what i can do. Thanks for all the info.

How did you go?

If leaning out the idle doesn't help, I'd make sure I'd bump up the timing for rows 400-1200rpm and keep the timing consistent across these rows.

That should eliminate the stumbles.

[Dennis93TA]

Well his MAF kept throwin codes so i disabled it and it hasn't had a problem since then. I know his tune needs work but he is trying to get a set of ported heads right now. So instead of fine tuning his setup that is gonna change soon, i'm gonna wait till he gets the new heads on. I'll take all the advice and apply that to his new tune. Thanks for all the help.