01 Z06 Cold Idle Hunting

[RKGarner]

Just got my Z06 back this weekend after having a H/C/I/TB installed. On cold start ups the idle hunts between 500 to 1200 rpm until the temp reaches 120. The motor will die if I don't help the throttle. After 120 the idle settles down to 900 rpm. The Tuner tell me it's the RevXtreme 90mm TB. Something about about 10% part throttle on start up? Any help or ideas on how to correct? Thanks RKG

[phils C5 vette]

unless you have a crazy huge cam, Find a new tuner

one guy who tuned my car told me the car is bucking and surging because of the way texas speed makes their cams.

your tuner needs to do more work on your throttle follower and throttle cracker

[RKGarner]

I also found the PCV and catch can plumbed backwards. I called him up and talked it over. He said he wasn't happy with the idle either and wanted to work on it some more. What tuning issues are there when the PCV is in backwards?

[phils C5 vette]

I switched my plumbing several times with the catch can before settling for what I have. there is a thread and pictures on here somewhere. Neither method affected idle.

[tblu92]

The ECM is in "open loop mode " at COLD starts --until coolant temp reaches 120* or 130 * then it goes into "closed loop"--- On warm starts when temp is already over 130* it is on a timer only -usually around 10 second before it goes into closed loop---This sounds more like what you are describing-
If it is only hunting/surging on cold/warm starts and then idles fine---I would have him work on the "commanded fuel open loop normal" table--before working on any of the idle airflow or throttle follower tables--if you make adjustments to airflow in open loop then it may mess up your closed loop idle and fueling--probably resulting in the opposite affect like having a hanging idle--

[RKGarner]

Thanks tblu92:
I took the car back on Tuesday and dropped it off in Dallas on my way to OK City for an FAA Seminar (Frontal Lotobomy)
The tuner worked on it Wednesday with no luck. I returned on Thursday morning to pick up the car and they were still not finished. They had come to the conclusion that it was the RevXtreme TB and wanted to install a Ported & Polished LS2 TB and then retune.
At the end of the day when all was done I drove the car home and could tell that the LS2 TB is a little sluggish compaired the the RevXtreme TB which was crisp in responds.
Got the car home and let it cool down. After 3 hours I went out and started the car up and the motor started it's cold idle surging until the temp got to 120+ and then dropped to 900 rpm. Unfortunately for me I live in Shreveport and there are no local tuners . The current tuner I'm using is 3 1/2 hour drive away. I have not called them yet to let them know how the car performed on the way home and that it will be coming back.

[tblu92]

If that tuner has EFILIVE--the scanning software has the ability to make "real time" adjustments while the engine is running or on start up---This is a great tool to sort out what you are describing--rather than just guessing at the open loop fuel--you can dial in an AFR and start the engine and see if the change helps--On my hds/cam shaner Tb-body car---I had to set the open loop starting fuel quite leaner--from the commanded 13.50-14.50 range, way up to the 15.75 to 16.00 range--Have him try and set open loop fuel at 16.0 with the real time tool and see what happens------He is deffanately on the wrong track But I would not be quick to critisize as sometimes myself I get stuck on a solution to fix a problem and until i get another set of eyes on it i can't solve it either---

[RKGarner]

Thanks tblu92
I found some great tuning information at this website. http://www.bowlingss.com/DownLoads/T...tuninginfo.mht
It helped me understand whats going on. I think what you have suggested is mention in this website information. Please take a look.
I have also sent this info to the tuner so maybe it will help him figure out a solution.
And I agree it does no good to critisize. That's going in the wrong direction. I actually think they are a great bunch of guys and are just have a mind block, so we will just have to work through it. I believe they are using HP tuners.
Thanks again
RKG

[Brian@RPT]

I tuned a 2000 C5 with a LS7 installed that had the same issue. The problem was it was too rich at idle and during cold starts. Now, it idles smooth even with a 248/254 cam The C5 uses a stock 90mm throttlebody as well. BTW Russell, nice Z

[RKGarner]

Thanks TX Vette,
I'm looking forward to Saturday when you can have a go at working out my idling issue.
Would like to get the RevXtreme TB back on if we have time.