Hanging idle.....what do you think?

[Slow73]

9108

Hope I attached my tune right? This is an LS1 transplant into a Nova, stock longblock, FAST 90/90 and the big Trex cam. Car idles good but when revved up off of idle, it hangs for maybe 6 seconds before it drops to an idle again. When its cold and I start it....it idles high for 10 seconds, flares up the drops down to a normal idle. Can someone look at my tune and give me some ideas? Thanks.

[WeathermanShawn]

9108

Hope I attached my tune right? This is an LS1 transplant into a Nova, stock longblock, FAST 90/90 and the big Trex cam. Car idles good but when revved up off of idle, it hangs for maybe 6 seconds before it drops to an idle again. When its cold and I start it....it idles high for 10 seconds, flares up the drops down to a normal idle. Can someone look at my tune and give me some ideas? Thanks.

On your 1st example (Hanging Idle), are you talking about Idle Characteristics when the VSS is zero? What happens if you are going 10 mph and just put the car in Neutral..do the Rpm's hang or do they drop?

On your cold Idle problem..what are the ECT's when this occurs.

As always it is trying to figure out what Airflow Table is Commanding at the time..

Edit..I wonder if Table B4314 is the culprit. That value would mean the Throttle Cracker would never delay?

[Slow73]

As for vehicle speed, it a ls1 swap with a turbo 350 trans, no VSS. As with all of my other car with no vss, its tricky coming to a stop but driving around and letting off the gas has always been fine. As for ect when this happens, dosent matter if it hot or cold, always flares up then settles down to idle. The hanging idle is bugging me....no matter what my ECT is, when the car is in park and you give it some throttle, even just a fast hit of the pedal, it revs and takes 8-10 seconds to idle again. Is there something I should try with B4314? I appreciate the help.

[Slow73]

Wow....b4314 looks way outta whack compared to my stock file......I cant even explain how that happened! Do you think I should try my stock values or something different?

[WeathermanShawn]

I have seen B4314 values like that in other LS1 years, but try using stock values.

Hanging Idle problems may be in the numerous Airflow Decay Parameters, so they can be tricky to track down. Looks like you have made changes in some of the Start-Up Airflow Correction and Decay? I try to leave a lot of those stock..you normally don't have to mess with them.

The only other thing I was curious about is B4501 & B4502. That effectively disables the Idle Learning Parameters. These are the Airflow parameters needed for the IAC to 'learn'. They are not related to LTFT, STFT in their function, so Open-Loop Tuning does not really require you to disable them.

Looks like you have reviewed the Idle Tips & Tricks, but any Airflow Table you can leave stock, makes tracking down these 'Hanging Idle' problems easier..http://forum.efilive.com/showthread.php?14439-Idle-Tips-amp-Tricks

Good luck..

[Slow73]

Ill try and return B4501 and 02 to my stock parameters. I can also try and return the start up and decay to stock too. I made a little progress, I removed 10% from my Desired Idle Airflow and it really helped my hanging idle. In park, im able to give it some gas and the rpm dosent hang anywhere near what it did. It actually dips a tiny bit below my desired idle rpm and catches itself then idles again. I do still have the flare up when cold or hot. Say for example, I drive the car for 30 minutes, shut it off.....restart it again after sitting 1 minute......it will idle high for a few seconds.....flare up say to 16700 rpm, the drop and idle normal.......any opinions on startup besides trying stock values?

[WeathermanShawn]

Ill try and return B4501 and 02 to my stock parameters. I can also try and return the start up and decay to stock too. I made a little progress, I removed 10% from my Desired Idle Airflow and it really helped my hanging idle. In park, im able to give it some gas and the rpm dosent hang anywhere near what it did. It actually dips a tiny bit below my desired idle rpm and catches itself then idles again. I do still have the flare up when cold or hot. Say for example, I drive the car for 30 minutes, shut it off.....restart it again after sitting 1 minute......it will idle high for a few seconds.....flare up say to 16700 rpm, the drop and idle normal.......any opinions on startup besides trying stock values?

Hot re-starts are always a problem. I usually relate that to fueling more than IAC. On restarts my IAT usually has shot up 30-40F (heat-soak) and runs choppy and lean for 10-15 seconds. Most of the Start-Up Airflows (B4304) do not add any additional airflow above 80C. If you have a lot of air in that Table, that may be causing your problem.

The only reason I ever advise stock is just to slowly eliminate every Table that might be causing a problem. You could always log every IDLE/IAC Airflow Pid..then using the Tune Tool track what Table the airflow is coming from.

But, that takes a lot of work..hence I go back stock first and work my way from there.

Let us know what you come up with..