Throttle Body Air

Definition: used to tell the EEC how much air in pounds per minute enters the engine through the TB at an idle

Platform:

Min Value:

Max Value:

Description:
TB airflow is a scaler the EEC uses as part of idle calculations. You need to change the scaler if you change TB, MAF calibraiton, or TB adjustment. And I do mean it is independent of idle RPM setting. It is a measure of how much air (measured in lbs/min not Kg/hr) your TB will flow with the ISC disconnected and the TB closed.

To get an optimum idle you want the TB to be able to just barely keep the engine running when the ISC is disconnected. If you have a big cam or a stroker you will probably have to use the set screw to open your TB a little more to achieve this. But then you may have to reset your TPS so it still reads < 1.0 V closed.

Your TB airlfow value should be equal to exactly one data point in your ISC aitflow function: the data point at the RPM where your engine idles with your ISC disconnected. This would be a low RPM well below your desired idle.

(It is strange that people talk about drilling a hole in their TB plate or putting on extra hardware to pass a little more air at idle, when there is a set screw adjustment right there. Just crank it open A LITTLE if you need more air - and then be sure to change your calibration so the EEC knows it flows more air when closed.)

Multiply the volume of air at you base idle setting by 2.205 and divide the result by 60. This is your "Throtlebody Airflow" scalar value. It is used to tell the PCM how much airin pounds per minute enters the engine through the throttle body at idle. The factory uses a 60mm TB and a 55mm MAF with a base idle fo 550. The stock combination will produce a MAF voltage of .615v at 550 rpm. USing the formula (MAF * 2.2046226 / 60 = TB airflow) you will see how the factory came up with the numbers they did. (stock setting of .55005). MAF transfer curve must be correct to use above formula, or your numbers will be wrong. Any time you adjust your idle, you need to recalculate this scaler. After this step, see "ISC Neutral Idle Air Flow" in "Functions".

Hints:

If you can't sustain an idle TB airflow is probably not the cause. I would look at:
1) Is your Injector Offset VS Batt "correct" for your injectors?

2) Is your MAF_Transfer known (derived from a flow sheet), or guessed?

3) Is your high Injector Slope "correct" for your injectors?