Where's a good starting point for cold idle surging

[99LS1SS]

edcmat-l1, would it make any sense to reduce the Default Injector Pulse width in the idle RPM range? Currently it is 1.277. Maybe drop it to 1.000?

Something that you've probably noticed already that I just made the connect on, when the STIT stops adding air at initial startup and transitions into removing air, it seems like right around that time, the surging starts.

[edcmat-l1]

edcmat-l1, how much after start enrichment fuel can I safely take out? Because, if that is causing the surging, then I'd be willing to 0 it out just to see if it helps.

I rarely have to modify that table if all else is right. But, you can cut it in half to see what happens.

[edcmat-l1]

edcmat-l1, would it make any sense to reduce the Default Injector Pulse width in the idle RPM range? Currently it is 1.277. Maybe drop it to 1.000?

Something that you've probably noticed already that I just made the connect on, when the STIT stops adding air at initial startup and transitions into removing air, it seems like right around that time, the surging starts.

Nah, you're way over that. IPW is in the 3.8-4.4 range while it's surging.

It's not the STITs. It's too much fuel. Look at your narrow bands while it's surging. They're over 900mv. WB is showing about 11.2:1. Once it starts to lean out, it stabilizes.

[99LS1SS]

You said surging is almost always too much fuel. What else could it be?

[edcmat-l1]

You said surging is almost always too much fuel. What else could it be?

It's too much fuel. Your IAC isn't making it surge. The timing isn't making it surge. It's too rich. The biggest swing out of the spark, airflow control and fuel control is the IPW.

[99LS1SS]

edcmat-l1, you inadvertently (or maybe intentionally) led me to what might have been the fix. I started it this morning and it didn't start on the first crank but, it did start on the second crank and it stumbled pretty bad until it finally got going. Once it got going it purred like a freaking kitten! It didn't surge one time!!! FINALLY! That is the first cold start with no surging.

You said "I rarely have to modify that table if all else is right." and that made me step back and think about this. All along I've felt like I was putting a band aid on a broken arm. When I set this car up I used Greg's injector data to get the injectors in the correct range. The only thing that I can figure is that the injectors have been modified or they are defective. I lowered the offset vs voltage table by 15% and I lowered the injector pulse with to 1 and the car did not surge one bit this morning.

I think the stumbling on startup can be addressed by upping the OL EQ table since I had lowered it so much trying to get the fuel out. What I've done is taken the stock table and averaged it with the current table and I'll see how it starts later today.

I might not have fixed the car yet but I feel like I won a battle this morning.

edcmat-l1, I want to thank you again for the help! I've learned more about idle in this thread than I ever thought I would. I sincerely appreciate you being patient with me.

I've attached the log from this morning. (the wideband isn't hooked up for this log so disregard the output for it)

[99LS1SS]

Here's this morning's log and tune. It stumbled on cold start and it had a little bit of surging but it is much better.

[edcmat-l1]

While it's warming up, it's in the 3600-3700 Hz range in the MAF table. Right when it switches to closed loop, it's still in the same range, and it pulls 10% with the STFTs. Then, as the idle comes down, so does the MAF Hz, and the fuel trims come into line. I would reduce the MAF table in the 3600-3700 range ONLY by about 7 or 8%. Try that, and see how it does.

[99LS1SS]

I've made the MAF change. I'll see how it does this afternoon.

What could be causing my stumble at startup?

[99LS1SS]

The MAF change seemed to help the transition from OP to CL. The only messed up part now is the stumbling on startup. How rich should startup AFR be?

[edcmat-l1]

I will post from a computer a little layer.

[99LS1SS]

I've played with the IAC and it doesn't seem to help. I'm going to add a little cranking fuel and see if that helps. My IAT's are a little high right now so I'm going to let it cool off some.

[99LS1SS]

Look what is missing from this log. It didn't surge on cold start!

Ed, I want to thank you again. When you told me to lower the MAF in the Hz range that it comes out of OL that made a difference. I ended up dropping it a little more and I didn't notice any surging on this start up.

This has been a hell of a learning experience and I appreciate everyone's help.