How do you reduce the "flare up" from Reverse to Park

[vortech]

Working on a Z28 auto and it has one slight problem-the rpm's flare up going from drive to park or reverse to park or from park to drive-what table is resposible for that?

Thanks!

[vortech]

Anyone?

[1998purplez28]

I have the exact same issues although after racing and coming to a stop my rpms go from 1500 to 500 sometimes shut off, or although it's bad to start a car with ac on if I do forget to turn the ac off before starting the car, the car will just shut off and then I turn the ac off and start the car again. I can't use the ac sometimes when the car is in reverse or it shuts off as well. So please if you run into what your problem is let me know. I Have posted my tune file asking for someone to look at it but no dice.

[SSUte01]

Cause for the issues is primarily a RAF issue, it sounds as though the adaptive idle is doing it's thing and zeroes out (as it should) during the transition from P/N to Gear and as your RAF (or fueling for that matter) is likely too high it will flare until adaptive idle can take care of it again.

This may not be it but I'm willing to bet it is a very large part of it.

Do an idle log and pay particular attention to your IAC, and STIT during the transition to and from Gear.

Inconsistent fueling can play havoc trying to nail issues like this down due their significant impact on Desired Airflow and therefore 'desired' RAF. This can be exaggerated at places like the track where heatsoak and high IATs etc can cause dicking fueling or the RAF may simply be off.

Have look or do you have an idle log to post up with Desired Airflow, fueling (be it WB or NB), STIT, IAC etc.

[1998purplez28]

Maybe you could explain a little more.

[gman4dx266]

On newer cars, GM's atleast, it doesnt matter about starting your car with the AC on, since the clutch isn't initially engaged anyways; it freewheels.

I too would like to figure this out. My truck flares to 1800 when I start the thing cold in the mornings, when the air temp is approx 55 or 60. Thats especially bad for me and my exhaust waking up the neighbors when i leave in the AM. The only way to make the revs come down is to shift in the reverse or drive, which is also uncomfortable because of the rpm change, which makes the truck lurch like im trying to dragrace in reverse lol

[1998purplez28]

Although I understand what your talking about with newer gm vehicle's and the ac, What happends is when you first start it up with the ac nob in the on postion, the ac is off and the vehicle trys to find a good place to idle shortly after the vehicle starts the ac compressor kicks on, at this point the engine hasn't found a good steady idle point, so the drag of the ac comming on kills the engine, once you turn the ac off and try and start it again, it takes a few cranks because of how much the engine is loading up. when it died.

[1998purplez28]

I have uploaded a log file.

[1998purplez28]

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[SSUte01]

That log doesn't have key idle PIDs such as STITs, LTITs, IAC etc.

Those LTFTs if accurate and your fueling in general will need some work, not a fan of LTFTs at all but horses for courses.

Have you got a crook knock sensor or knock sensor wiring as that enormous amount of timing being pulled will only exaggerate a dipping problem.

Like I said earlier it is a matter of nailing fueling as closely and consistently as you can and tune the RAF remembering that RAF is a base minimum so sometimes you will need to set this that the stable idle STITs suggest and then let the STITs pick up the slack when required.

That is about as much advice as I can give.
Cheers