Rough hot idle but smooth cold start

[Alex99]

Hi all,
I'm fighting with a rough idle when the car warms up above 68-70C ECT. It runs in OL all the time and is MAFless. Not exactly sure where I should start. I don't see any major changes at that temperature.
The engine starts fine when cold and idles really smooth without any rocking until it gets warm.
AFR is around 14.2 when warm. The car has a mild cam and ported heads and idles at 800rpm.
Thanks
Alex

[joecar]

What you need is in here:



Idle Tuning
showthread.php?4661-Idle-Tuning-Helpful-Info-Inside (http://forum.efilive.com/showthread.php?4661-Idle-Tuning-Helpful-Info-Inside)
showthread.php?14439-Idle-Tips-amp-Tricks (http://forum.efilive.com/showthread.php?14439-Idle-Tips-amp-Tricks)
showthread.php?5866-Auto-VE-questions (http://forum.efilive.com/showthread.php?5866-Auto-VE-questions)
showthread.php?14153-scan-tool-wont-log-rafig-or-rafpn (http://forum.efilive.com/showthread.php?14153-scan-tool-wont-log-rafig-or-rafpn)
showthread.php?14435-Need-help-Can-Start-Car-but-dies-when-I-give-it-any-throttle-before-going-to-CL (http://forum.efilive.com/showthread.php?14435-Need-help-Can-Start-Car-but-dies-when-I-give-it-any-throttle-before-going-to-CL&p=129519&viewfull=1#post129519)
showthread.php?7011-ETC-cars-and-IAC-parameters (http://forum.efilive.com/showthread.php?7011-ETC-cars-and-IAC-parameters&p=61455&viewfull=1#post61455)
showthread.php?14544-Working-on-my-idle-tune (http://forum.efilive.com/showthread.php?14544-Working-on-my-idle-tune)
showthread.php?14794-Help-with-open-loop-%28cold-start%29-tuning (http://forum.efilive.com/showthread.php?14794-Help-with-open-loop-%28cold-start%29-tuning&p=133446#post133446)
showthread.php?149-Idle-%28Transition%29-Tuning (http://forum.efilive.com/showthread.php?149-Idle-%28Transition%29-Tuning)
Stumble-3-seconds-after-cold-start&p=178921#post178921 (http://forum.efilive.com/showthread.php?14144-Stumble-3-seconds-after-cold-start&p=178921#post178921)

More Idle Tuning
showthread.php?t=149 (http://forum.efilive.com/showthread.php?t=149)
showthread.php?t=5866 (http://forum.efilive.com/showthread.php?t=5866&highlight=RAFIG)
showthread.php?p=86553 (http://forum.efilive.com/showthread.php?p=86553) post #17
showthread.php?t=2630 (http://forum.efilive.com/showthread.php?t=2630)
showthread.php?t=473 (http://forum.efilive.com/showthread.php?t=473)

Throttle Cracker/Follower
showthread.php?t=3568 (http://forum.efilive.com/showthread.php?t=3568)
showthread.php?t=4081 (http://forum.efilive.com/showthread.php?t=4081)
showthread.php?t=5406 (http://forum.efilive.com/showthread.php?t=5406)
showthread.php?t=5940 (http://forum.efilive.com/showthread.php?t=5940)

[Alex99]

Thank you Joe,
I'm familiar with some of these threads and checked out the ones I haven't read yet. I have set up my idle based on them already.
I couldn't seem to find anything directly related to my issue, though. I'm sure that there are many indirect influences but if somebody had a similar problem, maybe they can give me a hint where to start.
Thanks
Alex

[O1Z06]

Just a shot in the dark, is your idle speed set to one value, cold to warm.

Post a copy of your tune.

[minytrker]

Hi all,
I'm fighting with a rough idle when the car warms up above 68-70C ECT. It runs in OL all the time and is MAFless. Not exactly sure where I should start. I don't see any major changes at that temperature.
The engine starts fine when cold and idles really smooth without any rocking until it gets warm.
AFR is around 14.2 when warm. The car has a mild cam and ported heads and idles at 800rpm.
Thanks
Alex

Post your tune and list all your mods. A data log of cold and hot idle would also help. Its hard to help without knowing anything about your vehicle.

[Alex99]

14084

here is my current tune
Thanks
Alex

[joecar]

Alex

You should set C6001:P0103 to A:1-Trip

( and look for the immediate presence of DTC P0103 to let you know you are in fact running from the VE table )

[joecar]

Alex,

are you aware that the 1.000 cells in B3647 will be trimmed to using STFT's...? (this will mess up any attempts at correcting VE)

[joecar]

Hi Alex,

with a COS you can run adaptive spark (different values in HO and LO spark tables), just set A0002 to 100% (check it by logging ASPARK).

[joecar]

The hot idle problem may be related to the MAF not necessarily being failed.

[Alex99]

Hi Joe
thanks so much for following up on my topic.
I really appreciate the insight.
I've made all the changes but was wondering about your comment on B3647. Should I set it to .99999 or 1.00001 just to not hit 1? I would still like it to run around 14.7AFR.

Finally, does the tune make sense in general from what you can see, compared to other successful tunes? BTW, the Corvette has ported heads, mild cam, CAI, 9.5" billet converter, ported TB, ported LS6 intake, C6 Z06 exhaust etc.
Thanks

[joecar]

( I'm sorry for the delay, I'm slowly catching up on looking at people's files in detail, it takes a while to analyze each one )

Set the 1.00 cells in B3647 to 0.99 or 1.01 (i.e. 1% different than stoich) to avoid SOL trimming during tuning.

I'm still looking at your tune...

[Alex99]

No need to apologize...

BTW, here is my latest tune with the changes you suggested...

Thanks
Alex

14116

[joecar]

The other thing I noticed (and forgot to mention) is that the 105kPa columns of the two VE tables (B0101 and A0009) differ.

[joecar]

Which FPR do you have (manifold referenced or un-referenced)...?

[joecar]

VE table seems reasonable, boost VE table seems a little steep.

[Alex99]

Which FPR do you have (manifold referenced or un-referenced)...?

honestly, i don't exactly know how GM did it with the Corvette. The reference method is still stock, although I have higher flow injectors and updated the flow table accordingly.

[joecar]

So you have the stock fuel rail and fuel delivery system that came with your 2000 Corvette...?

[Alex99]

Thats correct.
Is there anything to gain with changing my current setup?
Thanks
Alex

[joecar]

Alex, I'm just sanity checking your IFR table

[ i.e. your C5 uses an unreferenced FPR, so the IFR table should be sloped, which it is ]

[Alex99]

Hi Joe,
after driving with the new tune that included your suggested improvements for a couple of days, I have to say that the rocking and roughness at idle is greatly reduced and the car drives very nice.
Thanks a lot! It was not much that I changed but it were definitely the right things.
Thanks
Alex

[joecar]

Hi Alex, good to hear.


One thing to note: if you're running MAF-less make sure that a MAF DTC code is present (this is how the PCM knows to use VE instead of MAF).