LTFT 16.4 for idle

I am stumped on this one. My LTFT is pretty much always at 16.4 when i am at 0% throttle.
This may not be a bad thing for gas mileage but it cant be good if i jump of the gas too quick when the motor is that lean.

LTFT locks in at 0 WOT every time and stays very close to that when i am on the gas at all.
It's deceleration and sitting idle that it almost immediately jumps to +16.4

What could be causing this? My buddy's regal does the same thing and this has had both of us perplexed for months now.

we both run different MAF's and have tried cleaning them. 02 sensors have been replaced. no or very little exhaust leak. no vac leak that i can find (though that would be my first suspect)
Do i need to tune it differently?

Are you talking idle in gear, or decel?

Tuning for decel is one of those difficult if not impossible things that I never figured out. My LTFT doesn't max at 16.4, but it's not always consistent, either. It might be at 5, or 8 or 10. I don't let it bother me, because tuning it wouldn't change the performance of the car. Using MAFF, you should be able to tune it for 0 LTFT at idle when you are on the brake (0% throttle) in gear. How does it do when you are on the throttle at medium and light throttle?

I have always heard of this issue at idle or deceleration, and have also heard its ok as long as it locks back in at 0 when applying throttle.

I think I've been away too long... Positive trim means it's adding fuel, right?

Why the hell would it add fuel on decel, when it's programmed to shut it off entirely if necessary?

Or, looking at it another way, +16.4 means it should add fuel, also called a "lean condition". I think fuel cut-off would certainly qualify as a lean condition.

(my guess: PCM ignores LTFT during fuel cut-off)

You did the IM gaskets and all that happy stuff in recent history? If the motor is clean and everything is sealed up properly, it really shouldn't be maxing out at lean LTFTs at idle. However, I've seen a few cars that just don't ever seem to wanna play ball. :/ It can be tuned out I'm sure. Probably not a huge issue as long as they bounce back to 0 when you add any sort of throttle.

yes LIM gaskets have been done and i used the high tq grey RTV when i did the I/C
It seemed to have started when i switched to the 42.5lb injectors.

Did you adjust injector flow rates to compensate for the larger injectors? If so, could be the injectors are just not precise enough at lower pressures (low RPM) to spray the finer mist.

^ What AA said.

Yes i did tune and change the PCM for the larger injectors.
I have read a few threads about how the larger injectors dont atomize the fuel as well and therefor dont idle as well.
Guess its something i will have to live with.

Matt, are you still living with this?

Honestly i have not check in awhile. Im sure its still off as my idle can be fairly rough. some sea foam every 6 months has helped though.
My money is still on dirty injectors and a 216k mile old fuel pump. lol

I think I am hot on the trail of mine, found a vac leak. I am curious if you are still seeing uber lean trims tho.