ALDL data logging

[Sgt Gus]

Idle will be higher in P/N. To me it sounds like somebody has modified the tune to bump the idle target, especially if the IAC seems to be moving around to maintain it. Mine is bumped to idle around 650-675 in gear and is probably around 850 in P/N. IAC counts don’t usually move much from park to gear, so with less load on the engine the idle goes up. And if the PROM is a tune, I’d wager that somebody also also modified the open/closed loop logic.

Edit - I see you have a 454. I am more familiar with 350. Some of the 454 had open loop idle as a factory tune. Also 454 idle speed target is 750rpm in drive fully warmed up and idle is open loop. This is all in the emissions and drivability manual. Sounds like you don’t have an issue to me with idle control via the computer

Ours is a 454 and functions as you described in the last paragraph exactly.
Have only started looking at data via WinALDL, 4800 baud, using normal pins NO 10k resister.
Also, still single wire O2 at stock exhaust manifold drivers side.

 

[gmbellew]

Ours is a 454 and functions as you described in the last paragraph exactly.
Have only started looking at data via WinALDL, 4800 baud, using normal pins NO 10k resister.
Also, still single wire O2 at stock exhaust manifold drivers side.

if it is working good as is, i wouldn't mess with it too much! Just keep it rolling!

 

[Sgt Gus]

if it is working good as is, i wouldn't mess with it too much! Just keep it rolling!

Yeppers, just want to make sure everything is working and correctly. Also, learn...

 

[YakkoWarner]

if it is working good as is, i wouldn't mess with it too much! Just keep it rolling!

Not looking to change anything (I figure Chevy probably knew what they were doing when they set it up) - mainly just wanting to know why it does what it does and when, so when it doesn't I am not floundering around. The 1000RPM+ idle when in neutral/park does worry me some just because dropping into gear or switching between drive and reverse seems to really make the tranmission banh pretty hard and my base instinct is "that can't be good for it"....

I know I have a weak injector throwing those intermittant lean codes - and now with the data stream I can see the BLM value creeping up. A lot of the reason I'm asking questions and such here and now is just to understand and learn what all is happening inside the black box.

 

[gmbellew]

Not looking to change anything (I figure Chevy probably knew what they were doing when they set it up) - mainly just wanting to know why it does what it does and when, so when it doesn't I am not floundering around. The 1000RPM+ idle when in neutral/park does worry me some just because dropping into gear or switching between drive and reverse seems to really make the tranmission banh pretty hard and my base instinct is "that can't be good for it"....

I know I have a weak injector throwing those intermittant lean codes - and now with the data stream I can see the BLM value creeping up. A lot of the reason I'm asking questions and such here and now is just to understand and learn what all is happening inside the black box.

If idle is 750 in gear. I’d expect idle in PN to be in the 9-950ish range. Maybe 1000. But certainly not much more.