strange idle problem

[QUICKSILVER2002]

Wondering if someone can help me here.

I have a c5 and have the tune dialed in pretty well (I have a pretty good handle on how most this stuff works), but the idle is still giving me fits.

It seems to not want to open the TB enough to hold a solid idle all the time. It is decent about 90% of the time, but then under just the right conditions it stumbles and almost dies. Those conditions seem to always include increased load (lights on, turning wheel....). And is more frequent as the throttle is just released, but sometimes happens in a steady state.

This never happens with the AC on, and I'm pretty sure this is because the desired airflow is much higher when it is on (TB is open a bit more with the IAC/ETC)

I have logged the condition several times and nothing really stands out as the problem except that the IAC desired airflow is just not high enough for the load.

My running airflow table is demanding about 9.5 g/sec, but the desired is only showing about 7.5 (maf and dyna-air is about 9.5 also). I'm pretty sure the idle trims are bringing the desired position down too much. It idles real strong (although a tad high) just after a flash and then it eventually drops the desired IAC airflow once the full idle learn takes place.

Like I said, with the AC on it idles like a rock (with the same RPM, but the desired airflow goes up to 9.5)

I've tried playing with the IAP table, but it did not seem to help (although I could have just done something wrong). I've also read quite a bit of info saying IAP has no impact once the motor is running (although this could be wrong, I know it has worked for some here, like what is stated in the sticky)

Anway, just wondering if anyone has any different ideas. I've tried just about everything. I wish I could log the idle trims (when is that going to be available?).

Also, what is a good timing value at idle. I’m wondering if I might have that too high, which is causing it to do a bad idle learn. I think I see about 19-20 adv at most idle conditions.

[bink]

I've tried playing with the IAP table, but it did not seem to help (although I could have just done something wrong). I've also read quite a bit of info saying IAP has no impact once the motor is running (although this could be wrong, I know it has worked for some here, like what is stated in the sticky)

Can you post your mods? Ported TB or 90mm TB?

The closer IACDES is to MAF Airflow the better mine runs. See gojo's sticky.

Sounds like maybe your idle trims are out of range. I think GMPX is working on these in V7 2.X.

[QUICKSILVER2002]

I've tried playing with the IAP table, but it did not seem to help (although I could have just done something wrong). I've also read quite a bit of info saying IAP has no impact once the motor is running (although this could be wrong, I know it has worked for some here, like what is stated in the sticky)

Can you post your mods? Ported TB or 90mm TB?

The closer IACDES is to MAF Airflow the better mine runs. See gojo's sticky.

Sounds like maybe your idle trims are out of range. I think GMPX is working on these in V7 2.X.

Car is far from stock, but TB is stock.

Mild blower cam 218/225 on 115. I also have a different fuel system on the car that is vacuum/boost referenced, but I have pretty much eliminated all that from being the problem.

I do have a manual Fan (high speed mode) override switch. If I turn that on the PCM does not know the fans are on and it does seem to make the problem worse (The extra IAC airflow for the fans is not set).

I’m almost sure this problem would go away if I could just get the idle trims to stop closing the TB so much. Like I said, it is perfectly happy when the AC is on.

I’m going to play with the IAP table a bit more tonight and see if I can make something happen. I think I am just missing something simple.

[GMPX]

Why not try changing {B4325} to 0 so it cannot reduce the idle learn........ahh, the idle PID's...sorry guys, one day we will actually get all this 'stuff' in!!.
In the meantime, the 2003 - 2004 modded O.S's should go up today. Does that excuse me for the lack of IAC PID's

Cheers,
Ross

[QUICKSILVER2002]

Ok, I think I figured it out.

My suspicion in my original post about the timing being too high was the key.

I was running about 19-20adv, I knocked that down to 15 and it is much better and IACDES airflow is much closer to actual airflow.

I’ve got to go back and try some other stuff now, but I’m pretty sure that the timing was my problem all along.

It feels good to finally make some progress on a problem like this

[bink]

Why not try changing {B4325} to 0 so it cannot reduce the idle learn........ahh, the idle PID's...sorry guys, one day we will actually get all this 'stuff' in!!.
In the meantime, the 2003 - 2004 modded O.S's should go up today. Does that excuse me for the lack of IAC PID's

Cheers,
Ross

You're the leader. The leader doesn't need excuses. :P

Autotune/BEN and the Custom O.S.s is like a 7 course meal. Not too big a deal that you haven't had time to pick up some croutons. Let's Eat!!

Cheers,
joel