TOP END REFINISHING

[XfireZ51]

Originally Posted by Paul Workman

Hi Dom,

Touched on something there...as I have idle hunting when the engine is real cold; at/near freezing or below. It goes away as the motor temp gets over around 60º - there abouts.

...and adjust if necessary so it is below the idle voltage threshold.

I'm with you until the term idle voltage threshold. I'm not sure exactly what you're referring to. Do you mean the TPS at idle; a la the 0.54V?? Not sure where I got confused...

Paul,

Most likely the motor is surging when cold because the Open Loop AFR may be too lean as the motor warms up. On modified motors, the warm up routine may need a higher rpm setting also. The IAC wants to close as CTS increases but it will open up to prevent stalling. So you end up w a seesaw effect. Then it will go into Closed Loop and stabilize. A while back, I posted a vid of my car going through the warm-up routine. If done right, the motor should go into C/L without much discernible difference than O/L.
As for the TPS, the calibration uses a value of >1% for TPS Position to indicate that the motor is no longer at idle. Mine is set at 1.17%. When you adjust the throttle stop, it changes the % TPS as a consequence. So as you make the Min Air adjustment, it's important to check that the TPS V is at or below the voltage the ECM considers to be idle. The calibration has an Idle Spark Advance that overrides the SA in the tables. That's so you get a consistent SA and it doesn't change as the MAP fluctuates. Especially an issue w cammed motors. On any motor, if the TPS V is above the idle setting, the ECM will use the SA in the tables and you could get a hunting idle which may be interpreted as a vacuum leak. Make sense?