At a Loss for Holding Idle after Startup

[Pur_SSyn]

I thought things were going well after reading through some tips on this forum, and uploading the changes.
Yesterday I went for a test drive which seemed like it would be ready for further tuning.

Today, the car will not hold idle (from a cold start). The engine fires up fine, and with some throttle will idle
nicely at 1200 RPM. After settling for about 45 seconds, the idle will hold itself at 1000 RPM.

The trouble is, if I snap the throttle, the RPM will dip to 500 and take a while to stabilize again. Once you're
into the acceleration, the engine feels great. I don't suspect any internal mechanical issues, and I've checked
for vacuum leaks around the intake & exhaust.

I'm uploading the tune that worked best (which is the one programmed before the camshaft and cylinder head
install). The scan is terrible; I know it's bad.

Using scanner controls, the AFR control is best around 12.7 for idle, and timing upwards of 25 degrees.

These are the cam specs:
http://www.compcams.com/Company/CC/c...csid=1440&sb=0

LCA - 109
Intake Center - 103
Intake Duration - 275
Exhaust Duration - 295

Short block is stock. 799 (243) Heads, and long tube headers. Installed billet Fuel rails (pressure 53 PSI).

Computer is 1998 PCM
Engine is 2001 LS1, T56 transmission
Stock injectors, stock MAF

maflwrpt8c_BEST.hpl < There's an error in the Adaptive Idle RPM, MAX ECT. Should be 234 degrees.
cruise_scan.hpl
trev_verify.hpt

I've tried everything from reloading the initial tune again, to starting over fresh using some of the "Big Cam" tips.


Any advice on holding idle would be appreciated. Thank you kindly!

[Pur_SSyn]

I think I'll be replacing the computer, and repinning the harness.

I've read enough horror stories with the 1997-98 computers to sway me, but moreso that we're using a 98 PCM on a 2001 engine which probably compounds my issue!

[Pur_SSyn]

The new 2001 PCM will be arriving tomorrow. As far as I'm aware, all of the sensors on this engine are 2001, but the owner cannot confirm.

He did have a different MAF sensor on the motor as he tried tuning out the rough idle in the past.

We will be using a newer MAF with the 2001 PCM, but I want to make sure all other sensors are compatible. My searches are
turning up empty, but if I find any info I'll link it here.

Is anyone aware of sensors that i MUST check before installing the 2001 PCM?

Thank you!

[2xLS1]

I looked at your tune and your problem isn't the 98 pcm. Your idle airflow and idle speed tables are stock, your VE tables are stock, your base timing tables are stock, over/under speed tables are stock. Your car is just untuned for the cam you installed. Your 98 PCM is more than capable of running that combination of parts. I'm also unclear of what the car is? There is a 2000 in your sig.

[Pur_SSyn]

I'll have to check those files because i definitely tuned the VE, idle tables, spark tables. Even messed with IFR, and MAF.

In any case I've repnned the harness, and new PCM is on the way.

My SS sold; the car I'm tuning is not mine. Its a 68 SS with LS1 conversion.

[2xLS1]

Not in the trev_verify file you posted.

[2xLS1]

Look at the fuel trims in the cruise_scan file. Your problem was not the 98 PCM.

[Pur_SSyn]

The cruise_scan file was based on the Trev_verify tune (which was the stock tune).

That was the baseline.

The best start and idle was achieved after several edits. That tune is not uploaded, but the scan associated with the final tune is shown as, "MAFlwrpt8c.hpl"

When i get back to my laptop, i can upload that file.

My only concern at this point is the sensor compatibility. We are not reverting back to the 98 PCM.

[2xLS1]

Don't bother. I wasted enough time looking at the crap you posted.

[Pur_SSyn]

Thanks champ, the fact that you totally ignored the question three times really highlights your ability, and aptitude.

Do you really expect me to rewire the harness, and send back the new PCM just to try some sh@t that I've already tried... and not have it work?

Anyone else that can answer the question, and not go back in time will be much more appreciated.

[Pur_SSyn]

Here are some useful links to close out this thread. The short answer is, the sensors are compatible aside from the fuel sender. Someone also suggested knock sensors.
I'll have to confirm whether the owner of the car has 2001 knock sensors, or 1998 (I'd think 2001, but I'm going to check to be certain).

http://ls1tech.com/forums/pcm-diagno...-99-pcm-2.html

http://www.hptuners.com/forum/showth...00-up-PCM-swap

[Pur_SSyn]

I wanted to update this thread for those "on the fence" about 1998 PCM's.

It turns out the car was mis-wired from the previous engine swap. The constant battery leads were not connected; rather they were
routed to the ignition relay.

This means (I believe) the PCM was losing memory every time the key was cycled. After connecting the appropriate pins to battery constant,
the car has been remarkably easy to tune, even with a high duration camshaft.