how to control startup RPM

[acric5]

I installed a 95mm throttle body on a c5 a4,
at cold start up the rpm goes to 2500 and comes back to 600.

I'd like like to reduce that start up rpm to 1500,
is there a table for that?

thanks
bill

[LS1_Dragster]

First, I'm no expert by any stretch of the imagination so take this accordingly.

With my 454 in the firebird I had a real bad issue with this and 2 things helped. 1) it was lean when it started and I found when it was lean the RPM's would shoot up then surge for a bit then settle down, more after start enrichment helped a ton. 2) airflow parked was too high with the aftermarket throttle body and by reducing this number it also helped.

Also, I found that if the idle screw it too far opened or even closed will cause the computer to over compensate. I monitored the IAC value until it was around 5-10 at idle and hot. I also found that turning off the car before making the idle adjustment seems to work better for some reason.

I don't know enough about what year/computer/operating systems to tell you were to go but find them and it should help.

Lee

[acric5]

thanks for the response,

I'm very new so please indulge my ignorance.

In LS1Edit there is a setting called Throttle Scale which I cant find in EFILive,

Also in one of the post on the forum someone referred to Idle Stepper Motor Park which I cant find either.

Perhaps someone knows how these are defined in my 2002 corvette LS6

Would, Engine Calibration/Fuel/Commanded Fuel When Cranking, limit the rpm at cold start up?

thanks
bill

[LS1_Dragster]

In my OS which may be different then yours but it's B4308 and B3632, the cranking setting wont help. Also if it has a high idle then B4307 too.

Lee

[mr.prick]

{B4307} can make RPM soar at cold start.
I had a shop "tune" my car before I had EFILive and this table
was increased across the board.
The car would start @ 1500RPM.

[johnv]

you need to log IAC counts and get them down to around 30-60 when hot by opening (to decrease count) or closing (to increase count) the throttle stop, the bigger throttle blade is letting through to much air at idle and the IAC valve is struggling to compensate.

[dfe1]

You're missing an important point. You installed a 95mm throttle body, and the PCM still thinks you're running the stock 78mm piece. The value in B4349 correlates throttle body area to electronic throttle control (ETC) motor position. Stock setting is .0255. I've found that as throttle body size increases, this value should decrease. There's some disagreement about this, but if you look at it logically, as you increase throttle body area, you need less throttle opening to flow the same amount of air. The command less throttle opening, you need a smaller number when you multiply throttle area by the value in B4349. You may also need to adjust the values in B5934 to control flare.

[acric5]

seems to work now

I dropped the throttle scale B4349 which I had at .019 to .017 and
I dropped the flare control from stock setting -5 to -25.


the start up is now controlled and doesn't go past 1000 rpm.

thanks very much, I'll get back if there are any adverse driving conditions that come up.