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[dogn]

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[Chris@HPTuners]

IAC position learns at idle, it has long term and short term trims you can log in the scanner. Long Term Idle Trim (LTIT) in Gear/PN/AC On/Off and also Short Term Idle Trim (STIT).

If your base running airflow has been tuned correctly you should see LTIT around 0 and STIT should also be small.

LTIT can take up to 5 mins to learn in each state. Idle Trims only learn when there is no follower or cracker active.

Fuel trims are the same although they learn a little faster.

[Chris@HPTuners]

how much is it moving? if it's only 1 or so thats fine, if the LTIT is moving by 2 or 3 then there's something not right there.

The idle trims learn to maintain the desired idle RPM, so anything that effects the idle quality will cause them to move a little.

[ElecTech]

After Drive, IAC counts are 0 both. LTIT -2.72, Desired Idle Air is now 3.67. Before drive Desired Idle Air was 6.62

This right here is an indication of what your problem may be.

Is this a cable operated TB?

My guess is that you have your throttle blade open too far, have drilled a larger hole in the blade, or have some sort of un-metered air coming into the mix. You should see your IAC counts at idle, with the least amount of load on, at about 40-60 counts. As Chris eluded to, the idle trims will adjust to try and maintain idle speed.

[SSUte01]

What tables make up Desired Idle Air? or How does the computer calculate "Desired"?


LOL, Google it huh.

Are you SD or MAF??

Reason I ask is that the accuracy of the airmass model has a massive affect on the 'desired' Idle Air as the PCM calculates it. To illustrate what I mean, make your car falsely rich (best illustrated in RTT but doesn't have to be) by increasing your 'airmass model' be it MAF/SD or both and you will see the Desired Idle value reduce and the inverse is true if you lean it out. Even increasing the actual Commanded AFR illustrates this, just not as well, use the scanner.

The PCM always assumes that Commanded AFR is Actual AFR, to it there is no AFR error. Now if your IAT/ECT bias is out or there are injector variables accounted for in your MAF/VE (which undoubtedly there will be some) or a host of other variables into your airmass model then you will see your desired Idle Air move around, the greater the inaccuracies the greater the swing. Gotta kind of hope that some the variables cancel each other out rather than compound.

Was the bonnet up when idling?

I will hypothesise about your situation you described above, idling in your driveway/wherever for an hour will cause pretty much complete heatsoak ie heat loss = heat addded to pretty much the all components in the engine bay including IAT, so this as we know generally causes you to be "lean" and this will cause a higher 'Desired" Idle Air. Now you go for drive and reduce some of the heatsoak and "richen" (not commanding richer just resulting in richer due to modeling errors) the car up and the Desired Idle Air has dropped and now the Closed Loop idle routines (I am talking about IAC here not fuel trims) is doing its best to get commanded idle speed to match actual which to you and me looks like trying to get your RAF to match Desired Idle Air, generally

RAF + STIT + LTIT = Desired Idle Air

This isn't strictly the best way to describe it because Desired Idle Air (idle speed error) dictates the Idle Trims not the other way around, but I hope I made sense so I guess it should be RAF = Desired Idle + STIT + LTIT but to keep simple we are talking about making Desired Idle Air the subject so I'll leave it for now.

For more stability get Desired Idle = RAF and without completely going off track = Airmass (MAF/SD), if the airmass isn't equal then that is indicative of modeling errors of which all cars will have some.

so for you I'm approximating your RAF but;

6.60g/sec (+/-0.10) + ~-0.2 (+/-0.25g/sec) + -2.72 = 3.67

I am guessing that your STIT was about -0.25 at the end of your drive and as the LTIT approached about 3g/sec the STIT would've been zero.

I am making quite a few assumptions on your setup here and as such could be miles off but what I would do is try and reduce/eliminate variables as best as possible and the biggest culprit I have encountered with the issues you are describing is accurate measuring of the IAT, so perhaps look into accurate repositioning (including rewiring if 5 wire) and/or faster thermistor. Then I would look at IAT/ECT bias and finally ensure your injector settings are as close as possible as all variables add up. Heatsoak would be my first place to look.

Again, lots of assumptions from me but hopefully some ideas to help you stabilise the PCMs modeling of airmass which ultimately drives the 'desired' Idle Air

Good Luck

[ElecTech]

I still think it is a mechanical issue. Sticking throttle, air leak, bad IAC, etc.

Possibly electrical, but not software related. IMO.

[69lt1bird]

Your TPS voltage is not correct. It should be between .45 and .55. If you get out of this range, the PCM uses data from a different fueling cell other than idle. Worth a try to back the voltage down, slot the mounting holes and rotate the TPS, you may have to cut a locator pin off.

After you rotate it and your DMM says the correct voltage, unplug the TPS, turn on the key, engine off. Turn off key. Plug TPS back in.

[Chris@HPTuners]

your IAC counts should not be going to zero, i never had to do an idle relearn on an LS1 (unless you do write entire).

[69lt1bird]

Just trying to give you advice from experience. You have this issue, trans issue etc. The TPS data is critical in all areas of the tune. Like Chris said, idle relearns aren't needed unless there is something mechanically changed, TB replaced, TB blade adjusted etc. Then you should only have to do what I told you early.

I know the manual well, I used to write them at GM plus a dozen years as a GM tech. .45 - .55 is a good target for idle voltage.

[MikeOD]

I am running 1bar sd enhanced, IAT has been relocated to front of car away from engine heat. IAT does not change much from the drive. Hood is up. I have changed IAC motors TPS sensors IAT sensors, checked amps/volts.

I question why you have re-located the IAT sensor.

Intake air temp is a very important part of your airflow model, this is why GM put the IAT sensor in the MAF sensor on newer vehicles. In order to properly monitor airflow, you need to know what temperature the air is AS it enters the engine...what temperature it is in front of the car doesn't matter...the engine is breathing the hot engine bay air, and your airflow model needs to be able to see/monitor that. What you're doing by moving it somewhere else, is trying to avoid the corrections that happen for the increased air temp, however, if those corrections were calibrated propelry, you'd see it's actually far more useful to measure that temp at the engine.

This is why on a turbo car, I ALWAYS want the IAT sensor between the intercooler and the throttle body. I'm measuring pressure in the intake manifold, I want my temperature measured in the same location.

Airflow models are only accurate if the data going into them is accurate.

Because you're doing this, I could see your idle tune going out of whack...as the engine heat soaks, it IS breathing in warmer air at idle, and the O2 sensors are seeing it, and the fuel trims are correcting it...but the IAT sensor is measuring the air in front of the car, thats not as hot...so your data that you're putting into your idle airflow tables, is wrong...now you take it for a drive, cool the engine bay down and get it closer to the temp the IAT is seeing, and the O2 sensors are re-correcting the AFR, and thus the airflow is way different than what you'd put into the idle airflow tables...and as it heatsoaks, it probably slowly comes back to where it was before all over again.