Rich closed loop idle

[RonSS]

Problem is the PCM is happy. It’s got everything right where it wants it to be, STFT’s are bouncing around 0, same with LTFT. Dashboard looks fine. I'm sure this is due to the camshaft overlap pushing a little O2 into the exhaust. The front O2 sensors see the O2, tell the PCM "hey were lean as hell down here" PCM dumps fuel until the sensors are happy again. Problem is that brings the AFR to about 13.75. This is measured with a 5 gas analyzer (California BAR 97 Smog Machine) I’ll bet this is a common problem and just wondered if anyone had an idea?....

Vehicle is an 02 LS1 Vette with the normal bolt on stuff. Cam is a 224/224 -114.

[joecar]

Ron, do you have a means of measuring Lambda or AFR...?

[RonSS]

2% CO is about 13.7 to 1 AFR. A little fat for Idle......:phatyo: Thanks for the reply.

Changed the first post from CO to AFR......

[RonSS]

Don’t know if anybody is interested or not but:

http://www.ls1tech.com/forums/showthread.php?t=670285

[Bruce Melton]

IMHO that rich idle is a fact of life as long as it leans out with more rpm, I would be happy, assuming you do not have smog issues.

Guess you ahve tried fooling with timing up to ~24* at idle? You can use Bidirectional to try it.

[RonSS]

The car does have to be smoged but we test at 15 and 25 MPH not at Idle so I think it would be OK with the rich idle. Actually I just got tired of the smell when stuck in traffic. Around here if you go out for a Sunday drive there is a good chance you will see some stop and go.

Bumping the timing up did help a lot, seems to like about 27 deg.

So far SSpdDmon’s idea is working for me. I have found that after forcing OL at idle if I change the AFR in {B3618} at idle RPM’s that is my “idle mixture screw”.

[joecar]

Yes, unfortunately So. Cal. is crowded on weekends (and on weekdays).

Let me know how it smogs.