Idle problem

[12sec.5.3]

In neutral after a rev idle hangs around 1200-1500 rpm's. How can I correct this to come back to idle immediately after a rev?
Thanks

[dfe1]

In neutral after a rev idle hangs around 1200-1500 rpm's. How can I correct this to come back to idle immediately after a rev?
Thanks

Take your foot off the gas pedal?

Seriously, it sounds like you need to alter throttle follower air flow, but we need a few more details-- engine specifics, recent changes, history. Has this problem existed for some time, or did it just begin after something was changed? Are you sure there are no vacuum leaks?

[12sec.5.3]

6.0 w/cam, headers, all bolt-ons. Recently went to the dyno and had someone else tune. That's the only change.

[dfe1]

had someone else tune. That's the only change.

You have found your problem. Assuming the engine runs fine otherwise, just do a compare between the previous and current tables that relate to idle air flow and spark. Something should jump out at you.

And just so I understand, your 12 second 5.3 is really a 6-liter???????

[12sec.5.3]

Oooops! No, I didn't have the 6.0 swap in mind when I created the screen name.
So your saying the tables should be stock?

[dfe1]

Oooops! No, I didn't have the 6.0 swap in mind when I created the screen name.
So your saying the tables should be stock?

Just pulling your leg.

The tables shouldn't necessarily be stock, but if the idle didn't hang before, then whatever settings were in the tune were obviously better than the current ones. When you compare the two, something should jump out. It could be that a few cells were accidentally changed, or that the tuner is "idle stability challenged". In either case, the problem should have been apparent and corrected when the truck was pulled off the dyno. On the other hand, if the high idle only occurs at specific temperatures, it may not have been obvious after the dyno session.

[The Alchemist]

Hi there, what you need to do to fix this problem, assuming you have a larger bolt on throttle body, is to rescale the idle controller steps vs throttle area calibration. The easiest way I have found to do this is simply copy the calibration from a Holden GTS tune ( this model had the larger throttle body ) and paste this into your tune and reflash. This is a good starting point and fixes most cars with idle hang problems.
This means that you can leave you throttle follower/cracker settings etc alone as this is a bandaid tweak to fix the problem.
By using the GTS calibration for a larger Throttle body you are telling the ECU that you are pulling more air into the engine per idle step opened than with the smaller T/B, this in turn adjusts all the other idle air calibrations/calculations automatically. Try it, it works a treat.

Mike

[Bruce Melton]

Mike,
I am chasing this issue from another perspective. I looked at the Holden GTS tune and B4349 in that tune is .0255. It that your reference?
Thanks,
Bruce

[SSpdDmon]

In neutral after a rev idle hangs around 1200-1500 rpm's. How can I correct this to come back to idle immediately after a rev?
Thanks

I'd bet money it's your throttle follower. Log it and see if it's still adding airflow after a rev while your idle is hanging. If so, you need to increase your throttle follower decay rates slightly to make it decay out faster. Small changes are good so you don't overshoot.

FWIW, I don't think the p/n decay rates are used. My car seems to think it's always in gear regardless of whether or not the clutch is pushed in. You should log your gear .pid (GM.GEAR or GM.PRND) to make sure you change the right tables.

[The Alchemist]

Hi Bruce, its still set at 0.0255, I never changed it, but this car had a manual T/B not an electric one.
Cheers,
Mike