Won't idle after hot start.
 

I posted this over on the HPT board as well. Well, I just got my VE dialed in, & have moved on to tuning the MAF, but have run into a problem that wasn't there before. After the car is fully up to temp. (oil temp @ 200), & I turn it off, if I go to restart it, it will fire up but not stay on. It idles for about 1.5 secs, then dies. I have heads, & a rather large cam, mods in my signature below.

Please help,
Tucker

I would up the desired airflow (RAF) a little for that operating temp range in order to keep the car running. Then log the STIT's and LTIT's from a cold start to dial it in. That's the most likely source of your problem.

what does your wideband say right before it dies?

Where can I find that in HPT? Next time I drive it, I'll log those, thanks. I have a feeling that it's because of my fans. I've noticed that when it dies, the fans are running, then turn off. Also, the car won't stay on with the a/c on, which of course turns the fans on automatically.

Sorry, no wideband.

Here is a screenshot of my Base Running Airflow

Please don't take this the wrong way, but tuning these things without a wideband isn't the best of ideas, and especially not if this is your first tuning project.

Could you also post up your OL coolant-temp correction table, and the start-up enrichment vs coolant table?

Try increasing and decreasing the MAF values by a point or two in the range where the car normally idles. Mine seems to have a harder time on start up with the MAF on as well, but other's cars that I've tuned didn't seem to share that problem. I'm wondering if bigger cams just don't play well with the MAF at idle?

Wow, those numbers are much higher than my base RAF values. Of course, different model year and a Vette.

yea, I'd agree with SSpdDmon.

Sounds like as soon as the start up airflow decays out she dies.
LTITs and STITs will become active above 176*F (80*C). Look for these Idle PIDS -> Engine-> Airflow-> Idle > LTIT in Gear and P/N and Idle Adapt (STIT).

From HP Tuners:

Idle airflow: Log the STIT and LTIT and add the 2 together. With a manual you will use LTIT in gear all the time, autos will use the respective LTIT depedning on the gear selector position. Add the 2 values together (or make a custom histogram) and make chagnes based on ECT. Say 30*C STIT is -0.30 g/sec and LTIT is 0.10 g/sec, you want to subract 0.20 g/sec from the 30*C cell in the idle airflow table. It is important to make these changes only from a cold start as they will give the most accurate data. Make sure it is logging and you make corrections in metric as it adds better resolution. For starters, adding 2 g/sec to the table before initial start up after a cam can help idle.

Here's a link ->http://www.hptuners.com/forum/showthread.php?t=3833

"Idle Relearn" is a big help with stabilizing your Idle with ETC. Basically, let it Idle above 176*F for 5 minutes and then turn the key to Off position for 15 - 20 Seconds. Then restart and let idle for a few minutes - until the Idle stabilizes. Do not use the Accel pedal on startup or during the Learn period (few minutes).

Good Luck. :)

I made a few changes to the RAF using RHS's spreadsheet. I guess it helped a little, but it still wants to die. I'm pretty sure it has to do with an accessories load being put on the engine. The reason is it only does is when my high fan is on, or I'm parralel parking, & turning the steering wheel back a forth fast. Idle drops down really low, & almost does, or does die.

Hell, when the a/c is on I have no chance of the car staying on. As long as I'm sitting there idleing I'm fine, but the second I give it gas, & the idle comes back down, DEAD. I've doubled my AC Offset Min - In Gear, & Max - In Gear #'ers, but it changed nothing.

hm... what is your desired idle speed? You might need to bump it up a little.

Desired idle speed: 875

.....

AC Offset Max in Gear:
bump it to -> 4.00 g/sec

Adaptive Idle Airflow Limits:

Max in Gear AC Off -> 3.00 g/sec

Min in Gear AC Off -> -3.00 g/sec

ST Adapt Airflow Max:

Bump it to 2.00 g/sec at all temps 60*C and above.

......................This should be a big help....expands your adapt idle air - LTITs and STITs.

Let it idle learn above 80*C for several minutes. Then turn on the AC and it will add in the neccessary airflow. After idle settles down the PCM will pull the added AC/On air from the STITs and offset (learn) the air into the "AC Offset Max in Gear" cell. You can scan and watch it happen. FWIW.

Good Luck,
joel

Thanks Joel!! I'll give that a shot today. :drive:

You're welcome. I'd have to agree with SMOKINV8 - maybe bump idle?? Off idle response will be a bit better if you bump it a hundred or two.:D