Idle Question

99 f-body

I have been getting conflicting answers from searching. I try to search first before I ask.

I had an issue of the car not idling well unless you hold your foot on the gas pedal. Well I decided to adjust the throttle cracker +2 around 0-40mph and 0 to 1600rpms. That was not enough, I then added +2 more around 0mph-0rpm to 1600rpm(idle area). The car started right up and my stalling went away. When I would drive it, and come to a stop, it would hang a little before rpm would drop, so I then subtracted -1. This seems to be a good spot so far.

I have read the the throttle cracker does not affect idle, then I read some say it does(I think Frost said it). Which one is it?

Is it possible that the throttle cracker increase did help the stalling problem by not closing the tb back after start up?

Cracker does not affect -stopped- idle. Not directly;
it's off, there. But the drop from cracked to closed is
a "stimulus" to the idle control loop and may expose
the loop's natural instability. This is the purpose of
the cracker profile, to produce a "soft landing". But
some cracker tables have crazy surfaces (spikes
and holes) which could easily kick something where
it hurts, get the motor started on dying before you
get to rest, etc.

Quote:

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Originally Posted by jimmyblue

Cracker does not affect -stopped- idle. Not directly;
it's off, there. But the drop from cracked to closed is
a "stimulus" to the idle control loop and may expose
the loop's natural instability. This is the purpose of
the cracker profile, to produce a "soft landing". But
some cracker tables have crazy surfaces (spikes
and holes) which could easily kick something where
it hurts, get the motor started on dying before you
get to rest, etc.

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You were right, adjusting the throttle cracker did not fix my issue stalling issue. I think I did not have enough spark timing and airflow and that fixed it.

Now I have a surging at low speed issue.

surging is usually a result of running rich. log your afr and see where it is

Quote:

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Originally Posted by printmanjackson

surging is usually a result of running rich. log your afr and see where it is

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It says 12.68-12.7

yep, you are way rich

You are way to rich I agree. I take it you have installed a larger duration cam? Check you IAC counts at idle. You can adjust your throttle plate to help the IAC not have such a range to cover. The motor in the IAC is slow and will over and under shoot causing the issue you are discribing.

I see this all the time here, people don't get the basics tuned in and start tuning other tables and it just gets harder and harder to correct or find the problem. You have to get the tune correct in the proper order or you'll just end up covering up the problem with another problem. I would put it in OL and force the AFR to the corrected value and see how it runs. Then find the cause that making it so rich. Large overlap with a big cam and running in CL causes this problem (just and example)

Quote:

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Originally Posted by mineralareatuning

You are way to rich I agree. I take it you have installed a larger duration cam? Check you IAC counts at idle. You can adjust your throttle plate to help the IAC not have such a range to cover. The motor in the IAC is slow and will over and under shoot causing the issue you are discribing.

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My IAC count is 137-142 at idle and 199 while driving.

NW 92mm TB, Stock LS1 TPS

IAC counts aren't that far out. Have you corrected the AFR?

did you get your afr dialed in? is this fixed? post your tune + log and a list of your mods so we can help better.

I will try and look tonight and see if I can help. can't look with this computer. got busy last night and forgot to look

if your iac counts are still 130-140 after you have the fueling in line - they are a little high. the iac counts needs to be about 70-80 when the engine is at operating temp. at idle. If you try and get the iac counts down only by opening the throttle blade and doing a tps reset the tps voltage will get to high which causes problems. you will have to enlarge the hole in the throttle blade (or drill one if it doesn't have one) to accomplish this. go in very small steps with the hole - you don't want to get it too big.

sorry it took me so long to look. your idle overspeed and underspeed tables are probably causing you grief. you have the underspeed table adding 4* at 0 rpm error and the overspeed table subtracting 4* at the same 0 rpm error - these both need to be 0* at 0 rpm error and then gradually add (underspeed) or subtract (overspeed) based on amount of rpm error. most tuners like to de-sensitize these tables (just a little) with bigger cams to keep them from overshoot undershoot (read surging) problems. the way your tables are set up has the pcm confused. :confused: