I was running against my friend in his '04 Z06 this pass weekend and noticed that when I got out of a run, the motor would idle real low. When I took it out of gear and let my foot off the gas, the tach would go to around 500 rpm and then bring itself back up to around 1K. It would do this about 3-5 times then be fine. My A/F (narrowband) looked fine so I am kinda stumped and don't know if this is normal. I have the fuel jetted a little rich and am only running a 100 NX shot.

Thanks

 

That seems to happen maybe once in a great while to me after spraying, the idle fixes itself right away, Im not worrying about it.

 

Sounds like the 02's are trying to catch up. The PCM is showing Lean/Rich.
This is guessing from my end. Any tune info would help.
Hawk

 

Wet shots do this a lot because of the "imaginary" fuel puddling in the intake manifold.
If you reference a wideband you'll see an extreme rich when it should be either a 14.6 AFR or into DFCO while this is happening.
It takes a few seconds for all the fuel to clear out.

 

eek... that would be bad if you got a intake backfire... lol

 

I am on the factory tune.

Thanks for all the input guys. If anyone thinks of anything else please let me know.

 

my wet kit has never done this [fwiw]

 

I thought the possibility of "real puddling" was bad enough...now we have to consider "imaginary puddling"... with wet.

 

yeah, just try hard not to think about it and stay on the button. Never lift.

 

Robert

 

This morning on the way to work I engaged my imaginary wet system. About 60 feet out, I nailed my imaginary button...about that time I yelled BOOM to simulate an intake explosion. Knowing I was going to be doing an imaginary nitrous run with my imaginary wet system, I threw the chunks of metal and plastic in the road to simulate my ripped up manifold. The addition of simulated fire was tougher...I just pretended it was there and called 911. When the Dire Dept arrived they took there invisible hoses out and put out the fire. By that point in time we were all simply shaking our heads at the imaginary carnage. It was a bad imaginary morning.

 

You shouldn't be talking about this in public.

 

Are you laughing with us or not? The comment about "imaginary puddling" deserves some discussion I believe...i frankly wasn't sure if it's a farce or for real. I don't think anyone should leave that sort of thing hanging. So please elaborate.

 

i thought it was funny

 

The over-rich condition when closing the throttle after using a wet kit is evidence that there was significant fuel still in the intake manifold. Liquid fuel would then be quickly vaporized because of the sudden pressure drop in the manifold when the throttle closed, and find it's way into the cylinder.

It's something that's hard to prove beyond any doubt without pictures or video.

 

Just listen to the exhaust back fire on a hard decel after a wet run, pop, pop and pop, extra/leftover fuel is going bye-bye. That's all the proof needed.
Robert

 

I love the occasional exhaust backfire I get sometimes on decel, especially on the street it scares the **** out of people.

 

Don't hate the wet people. Tuning with jets on dyno. should be helpful on the rich obviously factor.

I guess what's being said to your original question is that the motor takes a few seconds (at least) to realize that it's no longer seeing the extra volume of oxygen and gasoline. These systems are based on feed back from 02 sensors...run a:b air (with nitrous) /fuel for 12 seconds then idle at x:y air/fuel seems like it would take a moment to chill out.

 

Oh we're back on track


Then yes you're 02s and the PCM are trying to figure out you fueling needs.
This will happen whether or not the imaginary girlfriend is with you.
Hawk


Side note
Macon i think it's time for a nonsense thread.

 

When did the PCM start feed-back learning mode during WOT?
or did I miss that memo?