A little surging at startup....

[tinindian]

My tune is getting closer, just have a little bit of surging during startup. It starts fine and runs decent until it goes into closed loop, then the surging starts. After it warms up it idles great without surging. Desired airflow was set using mapped MAF method. Can someone give me some hints or things to try? Thanks.

[WeathermanShawn]

Is your Spark jumping around at that point?

If you are in closed-loop and your fueling is normal..I would look at the Spark Modifiers.

Could be ECT Spark, Cat-Spark, Idle Flare..a whole bunch of Spark Tables.

Probably not Airflow related..also your O2's can be pretty lazy at start-up. If you log enough of the Spark, HO2 pids it might give a clue.

Is your vehicle moving or parked when the surging occurs. Cammed car?

[tinindian]

Ok, spark maybe. I had not thought of that, I assumed airflow. I'll do some logging as you suggest. The car is stationary when this surge is going on and the cam is 226/230. Thanks.

[WeathermanShawn]

Yea, your cam is similar to mine (overlap).

You should be in Base Spark in Gear at this point..You should probably be running 22-26 degrees of BSIG (verify logging).

Let us know how it goes..

[tinindian]

Ok, I logged a "cold" start this morning and you can clearly see the surging from frame 400 on. Spark is locked at 27 deg and doesn't fluctuate during the surge. Let me know what you think.

[WeathermanShawn]

Yea, its always tricky. I see your RPM 'dancing' in the log..but why is always a little harder to figure out why.

You have multiple Airflow Modifiers that work in concert with the IAC and how much the RPM swings. You have probably followed the Idle Tutorial exactly, but here is a refresher.

Airflow Modifiers:

B4352
B4504
B4512.B4514,B4515

If everyone one of those have been tuned via the Idle Tutorial, then I would compare every item changed on your tune vs stock. Are you adding (or subtracting air) in any other parameter?

Is your TB stock? IAC altered?

Your O2's are also a little lazy on start-up..so are mine..how long ago do you swap out for new ones?

Thats about all I can think of. I know SSpdDmon has done some additional work on Idle Tuning..might check with him if some of these tips do not work.

[tinindian]

You mentioned airflow modifiers & the IAC. But I logged the IAC and it's steady thru surges. Note the injector duty cycle is swinging with the surge but no air is being added with the IAC. How the hell can the rpm go up w/o additional air? What am I missing? Maybe I should take everything back to stock and start again!

[WeathermanShawn]

Yea, I am having a hard time knowing exactly what frame number(s) you are talking about.

Are you talking about your IAC Steps?

I see some air from the TF being added, but I think that is when you are blipping the throttle.

I see your MAP swinging around, so obviously your Vacuum is swinging around.

I guess if I compare your Idle to mine, your O2's are very slow at Idle and my fueling stays pretty much at stoich. My MAP stays rock steady.

Has your Idle always been this way?

[SSpdDmon]

Funny, I would have bet the IAC is jumping around if the spark is locked in. Did you change any of the idle airflow characteristics for the IAC or are they all stock (except the desired idle airlfow)?

The other option would be to raise the ECT at which the PCM switches to closed loop. As long as your tune is close and you're not hoppin' all over the throttle on a cold motor, that should be a perfectly fine solution.

On the other hand, I'd be hesitant to run closed loop on a cam'd application with significant overlap. You're just going to be dumping in a bunch of fuel at idle. I don't think it'll be "too much" in the sense that it causes long term problems. But, it'll affect your wallet over time.

[tinindian]

Yea, I am having a hard time knowing exactly what frame number(s) you are talking about.

Are you talking about your IAC Steps?

I see some air from the TF being added, but I think that is when you are blipping the throttle.

I see your MAP swinging around, so obviously your Vacuum is swinging around.

I guess if I compare your Idle to mine, your O2's are very slow at Idle and my fueling stays pretty much at stoich. My MAP stays rock steady.

Has your Idle always been this way?

Ok, the IAC opens up at startup then drops slowly until frame 280 and then it stays at about 110. Then the surge starts at frame 400, the IAC doesn't move but the injector voltage fluctuates. I don't touch the throttle until about frame 1200. Has my idle always been this way? Well I just fired the new motor w/ rebuild, cam, & ported heads a couple months ago but it's been kind of goofy from the start. I had a low-buck mail-order tune to start and I've been tweaking. Thanks for the help.

[tinindian]

Funny, I would have bet the IAC is jumping around if the spark is locked in. Did you change any of the idle airflow characteristics for the IAC or are they all stock (except the desired idle airlfow)?

The other option would be to raise the ECT at which the PCM switches to closed loop. As long as your tune is close and you're not hoppin' all over the throttle on a cold motor, that should be a perfectly fine solution.

On the other hand, I'd be hesitant to run closed loop on a cam'd application with significant overlap. You're just going to be dumping in a bunch of fuel at idle. I don't think it'll be "too much" in the sense that it causes long term problems. But, it'll affect your wallet over time.

If I'm looking at the right PID (GM.IAC) it stays steady. B4403 is stock but I've tweaked idle parameters per the tutorials by you & Shawn. I'll do some playing with open loop. My cam only has 2* overlap which isn't too significant but it won't hurt to explore. That's what I find interesting in tuning - I think I have something figured out and then someone throws something else out there I just have to play with. Thanks.

[WeathermanShawn]

Most of my Idle advice is more general than specific. I always think it is best to make sure there are no mechanical issues (vacuum leaks) or if there are non-stock parts such as different size/make of TB or Intake that may be causing the issue.

Secondly, the more 'little' changes one makes from stock (Idle-wise), the harder it come be to diagnose where the issue is coming from. Thats why I try to follow SSpdDmon's Idle Tutorial exactly,..http://forum.efilive.com/showthread.php?4661-Idle-Tuning-Helpful-Info-Inside followed by the Idle Tips & Tricks:http://forum.efilive.comshowthread.php?14439-Idle-Tips-amp-Tricks (http://forum.efilive.com/showthread.php?14439-Idle-Tips-amp-Tricks)

Rarely have I ever heard from anyone who as tried ALL of those Tips who does not have a decent Idle. A lot of people short-cut, thinking [ ..well that part does not apply to me..].

I use closed-loop for my vehicle, with about 10 degrees of cam overlap. But some vehicles would rather stay open-loop as fueling consistency can become challenging as the cam gets bigger. So you might re-consider closed-loop if that is the culprit.

Sorry I can't be anymore specific about your issue. Back to stock, follow every Idle Tip in the Tutorials..if you have really already done that, there is probably another issue..not tuning that is causing your problem.

Good luck..

[tinindian]

Update - I went thru the original idle tutorial again as Shawn suggested, comparing the settings I had vs. stock. Apparently I had adjusted Learned Airflow Correction & Direct Airflow Correction a little more than the tutorials recommended. I also backed idle timing down a bit and now it starts & idles great. Thanks Shawn & SSpdDmon for getting me squared away. :cheers:

[WeathermanShawn]

Glad to help.

Its always good when you 'follow the recipe'.

Good work on sorting it out!:)