Car dies on initial startup when cold

[Skinny]

When the car (99TA, LS1, 4L60E, BIG cam) is cold, it dies immediatly after startup unless I hold the throttle open. For the first minute or two, I have to "two-foot" it to keep it alive. I searched through here and found several threads where people had similar issues when it was hot, but not cold. Once my car is warm, it will start and idle fine with no issues. Ideas?

current tune attached

[MMGT1]

Looks like your commanding 11:1 AFR @ startup. Maybe a bit much. I'd try setting your Start up Initial Adder vs Coolant Temp to 0.175 from 8* to 56* too see if it likes that.
Are you getting a really rich smell @ start up when it's cold?

[Skinny]

Hell, I get a really rich smell all the time... I had someone tune the car for me when I first built the motor and since then all I've been dealing with is the automatic trans shifts (thanks for your help in the other thread, BTW). In the year I've had this software, I've never once looked at the engine stuff until yesterday. I'm still kinda feeling my way through that. I'll make the changes and try it out.

[Skinny]

Much better. It didn't die immediately, but it does still struggle to hold it's idle. I logged the cold start. I let it idle for several seconds, gave it a little throttle, then put it in gear. A quick tap on the throttle in gear then it died. here's the log if this helps anyone.

[MMGT1]

I aim 12.5:1 for start up which would put you at 0.150 in the cold range of the above table.

[Skinny]

I made the above mentioned changes, it holds an idle, but much lower than the target. It's also kind of touchy. A quick stab of the throttle and it will not find it's idle on the way back down and die. I enabled the STFT during open loop yesterday to see if it helped at all. It didn't, but it is still enabled. Should I leave it or disable?

[SnakesRslow]

Much better. It didn't die immediately, but it does still struggle to hold it's idle. I logged the cold start. I let it idle for several seconds, gave it a little throttle, then put it in gear. A quick tap on the throttle in gear then it died. here's the log if this helps anyone.

try increasing your "base running airflow", "Friction airflow initial", and "startup airflow initial" in the ECT range's you are having issues with. I would start with making 5-10% increases

start with the baserunning airflow... engine>idle>idle airflow

[Skinny]

I've made the recommended changes and still had some issues. It would idle without me holding the throttle but it was 500 rpm or so below the desired idle. I finally looked at the IAC position and it was maxed. I asjusted the throttle stop until it idled well and brought the IAC position around 165 and it fires up and idles great, however now the TPS is at 2% (.86V). What's the cure here besides drilling a bigger hole in the TB blade?

[SnakesRslow]

I've made the recommended changes and still had some issues. It would idle without me holding the throttle but it was 500 rpm or so below the desired idle. I finally looked at the IAC position and it was maxed. I asjusted the throttle stop until it idled well and brought the IAC position around 165 and it fires up and idles great, however now the TPS is at 2% (.86V). What's the cure here besides drilling a bigger hole in the TB blade?

im not 100% but i believe the base running airflow is the alternative to drilling a bigger hole

[Skinny]

im not 100% but i believe the base running airflow is the alternative to drilling a bigger hole

I hope so.. it's got a pretty big hole in there already.. a little over 1/4"

[12secSS]

How big is a "BIG CAM"? I am still using my stock throttle body on my F13 cam, but my IAC steps are at 120 with the stock size hole.

[Skinny]

244/249 .610/.613 109LSA

Should I just keep increasing the base running airflow until I see results? I left the throttle stop at 2% and let it warm up. After it was hot it idled very high until I closed the throttle stop to 0% (.76v)

[mike01z]

try doing this also as it seems to have helped me more than RAF and everything all though all those things did help me.

On the VE table take the 400 800 and 1200 colums and make them a tad leaner, start off like maybe 5 percent or so, so multiply them by .95 if this seems to get better but doesn't fully do the trick then take the 400 and 800 colums and multiply by another 5% or .95 and do the 1200 by .98 or so.

Obviously if you go too far it gets too lean.

[ElecTech]

Another thing you may want to look at is your Idle Underspeed Spark table. There are no values below -175 rpm. With a cam that big, you could see a 175 rpm swing pretty easy and then lose any underspeed timing assist, especially if your seeing it 500 rpm below. This may also help your IAC as it won't need to try and "save" the idle with airflow alone.


P.S.: That is a pretty big cam! Is that stock displacement? Do you have ported/aftermarket heads?

[Skinny]

Thanks, I'll give all that a shot today.

As for the car, stock displacement and the heads are the bottle-neck at the moment... they're "near stock"

[mike01z]

I also messed with my over and underspeed spark table I only give mine about 5 degrees of total spark leway up and down. that stabalized my spark, also zeroing out the ECT spark retard table, tuning the RAF helped but the ultimate thing that really clears it up is the VE table. I had to make mine a decent amount leaner to get it to idle really at all.