Changed to LS2 90mm on LS6

[Rusty]

I have changed to the new FAST 90mm big mouth intake over a LS1 engine. We have bought and installed a conversion cable to use the 2001 Corvette C5 wiring harness with the LS2 Throttle Body. Our 0911 PCM (OS 12220588) is set to GM factory calibrations for the LS6 78mm Throttle body.

I am experiencing some rough idle conditions and I am eliminating possible problems. Table B4403 (IAC Effective Area) only goes to 120 square mm.

What is the best way to adjust the calibration for this situation? I figure a 78mm throttle body should have a square area of over 4700 sq. mm

What am I missing?

Also, I do not think this is why I am having rough idea conditions. Which table should I modify for a newly installed larger lift cam. No idle problems before the new cam and we had the LS2 throttle body installed before.
New cam specs:
lift .647 intake and exhaust
250 duration @ .050

[mr.prick]

I`m not too sure how you would even go about tracking this table,
there is no square mm PID that I can find.
B4307 and RAFIG is where I would start.

[5.7ute]

IAC effective area is the area available between the IAC valves pintle & orifice in relation to steps. This will not need modifying unless your new throttle body has a larger orifice in its seat.

[Rusty]

Thanks 5.7ute... I will change values back to stock. I and try something else as the problem.

[Kurtomac]

B4349...what are you guys inputting in this for your LS2 Tbody on a LS1/6 car
seems to be confusion there from my searching...some go larger number...some go smaller

[dfe1]

Smaller seems to make the most sense and has worked for me in a number of instances. The description states, "Used to convert a desired throttle area from square millimeters to ETC motor position". Also note that the units are expressed as "% per square millimeter". To me that implies that you need less percentage of throttle opening from a larger throttle body than from a smaller one to maintain the same amount of air flow. In essence, this number doesn't relate directly to throttle bore diameter, it relates to open throttle area per degree of throttle opening. A larger diameter throttle body presents more open area at the same degree of opening as a smaller throttle body, hence it should be open less to maintain a given idle air flow. Consequently, a smaller number in B4349 is required for a larger diameter throttle body.

To test the theory, just increase the value in B4349 (without changing the throttle body) and see what happens. When I did it, idle speed would take quite a while to return to commanded after releasing the throttle.

[Kurtomac]

DFE....how much desired air did yours require?....mines way higher than some other I know of....but they went the other way with .0320 thus the lower desired air number....mine is like 17.6

[dfe1]

DFE....how much desired air did yours require?....mines way higher than some other I know of....but they went the other way with .0320 thus the lower desired air number....mine is like 17.6

My set-up is a bit different-- still running a ported 78mm, but desired air flow at normal operating temp is 9.0. Desired air flow doesn't live all by itself-- there are a few other considerations. What is your measured air flow at idle? If it's considerably less than desired, the data in other tables is biasing things. Also, what is your commanded idle speed?

[Kurtomac]

how do i find measured air flow at idle? my idle speed is 950

[dfe1]

how do i find measured air flow at idle? my idle speed is 950

In the Scanning tool, just monitor the MAF readings at idle. The PID is "Air Flow Rate from Mass Air Sensor. Make sure the PID is set to the same type of units as you're using in the tuning tool (Hopefully grams per second). If you're running speed density, you may have to use the calculated air flow PID.