Cannot change idle speed on E38 PCM

[njedwardz]

Hey all,

I'm working on the idle tuning on my 2013 Corvette A6 that I've recently had a cam put into. The idle is pretty much perfect now but it's idling a little high for me. The issue is, no matter what idle speed I command in the tune, the PID "GM.idlerpm" (which is "desired idle speed") remains at 896 (which is its version of 900 RPM). I CAN go into the DVT tools and command it lower, but obviously this isn't a real solution.

To be clear, the issue isn't that I have too much airflow and the car won't hit the commanded speed; it's that the car is not commanding the same idle speed that I am...For example, whether I set the commanded idle RPM to 900, 875, 850, 700, etc. the PCM will not command anything lower than 896 unless I manually force it do do so through DVT. Commanding higher values DOES work as my idle speed after start table IS working as programmed until it reaches any number below 900.

This is a new issue - idle was fine at ~600 RPM before the cam.

Anyone ever experienced a similar issue? Solutions? Tune file is attached. Will try to record/upload a datalog of what's going on as well when I have a minute.

I'd appreciate any help! Thanks in advance!

[Taz]

That tune has been HIGHLY modified, and this was NOT done with EFILive. Whoever set it up, set the minimum commanded Idle Speed to 900 RPM. Take it back to your tuner, and have them adjust it to your requirements.

[njedwardz]

I had a little bit of a feeling this might be the case. They gave me the whole "anything you can change with HPT can be changed with EFI line....unfortunately my installer is a little bit of a drive away, and I have exams for the next 2 weeks. While I know they would be happy to make any changes I want, I'd rather not have to wait lol.

How heavily modified are we talking here? Meaning, could I just take one of my pre-cam tunes (one never touched with HPT) and copy over my current idle, spark, fuel, airflow, etc. tables and just run on that?

[Taz]

Historically, HPT never had any type of VVE tables that were native to the software - VVE tuning required a third party software, and jumping through a few hoops. This is lent itself to "MAF only" tuning with HPT - which was what many had come to expect.

HPT recently added native VVE tuning to their software. The tune you posted is actually an attempt at an SD (Speed Density) tune, but was not setup optimally.

I would recommend working with your tuner. No sense in having bad things happen, simply because you were impatient.

[njedwardz]

The tune I posted is not the tune that was on the car when I got it from the installer. I've set it up to be SD so that I can work on the VVE myself - if you'd like I can post my most recent pre-can tune, as well as the initial tune from the installer.

What's sub-optimal about the SD setup I'm running now? Just wondering so that I can get it right lol. I had very good luck doing VVE tuning with this setup before the cam.

Essentially, the installer just set me up with a baseline tune to have the car running when I picked it up. I had wanted to just do the tuning with them myself from the start, but due to time constraints we had to do it this way.

[njedwardz]

Please see the two tunes I've attached here. The one labeled "NJE cam tune 0" is the final tune I had on the car BEFORE the cam went in. The other tune "BHR cam tune 1" is the tune that was on the PCM when I picked the car up from my installer (i.e. the tune that they flashed in).

From what I can see, it doesn't look like they altered any of the spark, MAF or airflow tables. They mainly messed with idle (although not much from what I can look at with EFILive) and a couple other small things. All differences between the "BHR cam tune 1" tune and the tune I posted in the first post were made by me with EFILive.

Mind taking a look and seeing what else they changed in HPT?

I really appreciate the support!

[Taz]

Sorry - I have neither the time, nor the inclination, to go through other people's tunes line by line.

I do my best to keep people from needlessly chasing their own tail - like telling you that the 900 RPM idle issue was based on a parameter changed by another software (in this case HPT).

If you want to try and tune this vehicle yourself, then search this Forum for a VVE & MAF tuning tutorial (and PDF) by Swingtan. There is also a great E38 Idle Tuning thread by started by Hymey, with contributions from Swingtan.

[njedwardz]

Got it. Thanks for your assistance up to this point.

the VVE/MAF/idle tuning I've done so far (both pre- and post-cam) were done in accordance with the guides/threads you mention - I've had a great deal of success with these methods according to my WBAF readings, but if my setup is not correct or could be improved further I'd love any input you have.

Again, I appreciate the help.