TOP END REFINISHING

[XfireZ51]

Originally Posted by mike100

All you need to do is make sure your TPS is set to the indicated voltage at zero percent opening (about .54v if i recall). The IAC counts are probably 0 if it can't make it run slower than 1k rpm.

you either had a line pop off during reinstallation (or a mistake in tube routing), or your throttle body blade redo got messed up a little. Just seems like too much air. maybe you should double check the throttle angle and not the electrics.

Mike,

Yes I know about setting the TPS v, but that is affected by the Min Air adjustment. You need to get the throttle blade opening correct before you can set the idle TPS voltage properly. It's an iterative process.
Turn the key ON, then pull the IAC CONNECTOR. This should block the IAC port to the throttle body. Then start the motor. Does it idle, and if so at what RPM?
If it's too high, you need to close the throttle blades till you reach the desired idle speed. You actually set it a bit lower so you get some IAC control over the idle. Whenever you adjust the throttle blade, need to re-check TPS voltage and adjust if necessary so it is below the idle voltage threshold. Otherwise, ECM won't use the correct Spark Timing and you end up w an idle hunt.

[Schrade]

Originally Posted by XfireZ51

Mike,

Yes I know about setting the TPS v, but that is affected by the Min Air adjustment. You need to get the throttle blade opening correct before you can set the idle TPS voltage properly. It's an iterative process.
Turn the key ON, then pull the IAC CONNECTOR. This should block the IAC port to the throttle body. Then start the motor. Does it idle, and if so at what RPM?
If it's too high, you need to close the throttle blades till you reach the desired idle speed. You actually set it a bit lower so you get some IAC control over the idle. Whenever you adjust the throttle blade, need to re-check TPS voltage and adjust if necessary so it is below the idle voltage threshold. Otherwise, ECM won't use the correct Spark Timing and you end up w an idle hunt.

Got it there Dominic; will start there in the AM. I was tentative about playing with that, to be able to reverse any adjustment.

Y/T - best I could do this time... I need to change DM window font...
http://www.youtube.com/watch?v=J_9VApesl_o

Originally Posted by Z06scentair

Sounds good have you had it on the street yet? Curious how the auto will do in the car?

Auto runs fine Z06, although I can by no means rule out EMI interefence in this hesitation diagnostic issue. SOME circuit 'sings', in sync with TPS range of motion - best I can describe THAT. I can catch that in a vid too, but if anyone can make anything of it, I'll be HAPPILY surprised...

Originally Posted by mike100

All you need to do is make sure your TPS is set to the indicated voltage at zero percent opening (about .54v if i recall). The IAC counts are probably 0 if it can't make it run slower than 1k rpm.

you either had a line pop off during reinstallation (or a mistake in tube routing), or your throttle body blade redo got messed up a little. Just seems like too much air. maybe you should double check the throttle angle and not the electrics.

Understood Mike; DM does indicate 0% TB opening, but again, Min Idle adjustment might come before TO % confirmation.

[mike100]

If you didn't break the adjustment on the throttle stop, that's probably not your issue. I would do what you have to to read the IAC count value on your data stream. (or pull the IAC plug as suggested above).

Lets not make it complicated beyond that. There seems to be a fundamental air leak. it is often suggested to take a stiff binder book cover or similar and block off the air horn (accordion duct removed) while the engine is idling to try to stall it. if it still runs, you can often hear the point of the air leak under the plenum.

[efnfast]

Schrade, did you clean the slimy stuff out of the throttle body,around the plates, nice and clean now?

[XfireZ51]

R U saying you did re-install the throttle blades? The stock throttle stop stud uses an Allen wrench for adjusting. As Mike pointed out, GM didn't mean for this to be adjusted, but hey this is 20+ years later and things wear and go out of adjustment. These motors are being modified including the throttle body. The point is to check that all the basic mechanical components are working properly before chasing a vacuum leak. It's A PITA which is why several of us have replaced it w an 8mm hex head bolt. One thing to do is take a .002" feeler gauge and see if it drags w the throttle blades closed. A strip of paper will work also. It's a close approximation of where the blades should be with a stock motor. Make sure the motor is up to operating temps before you check on IAC counts and/ or decide to adjust the Min Air.

[Paul Workman]

Originally Posted by XfireZ51

Mike,

Yes I know about setting the TPS v, but that is affected by the Min Air adjustment. You need to get the throttle blade opening correct before you can set the idle TPS voltage properly. It's an iterative process.
Turn the key ON, then pull the IAC CONNECTOR. This should block the IAC port to the throttle body. Then start the motor. Does it idle, and if so at what RPM?
If it's too high, you need to close the throttle blades till you reach the desired idle speed. You actually set it a bit lower so you get some IAC control over the idle. Whenever you adjust the throttle blade, need to re-check TPS voltage and adjust if necessary so it is below the idle voltage threshold. Otherwise, ECM won't use the correct Spark Timing and you end up w an idle hunt.

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...

[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?

[Schrade]

Originally Posted by XfireZ51

Have you set the Min Air adjustment? When you get DM connected, what is IAC doing at "idle"? How many IAC counts? What does "TPS calibrated"mean? What is the coolant temp as it's idling? Why do you think you need new injectors?

Cold motor; idling STEADY @ 900.

DM IAC says 150.

[Schrade]

Do I pull the IAC BEFORE, or AFTER adjusting Min Idle stop screw?

[Schrade]

Originally Posted by mike100

If you didn't break the adjustment on the throttle stop, that's probably not your issue. I would do what you have to to read the IAC count value on your data stream. (or pull the IAC plug as suggested above).

Lets not make it complicated beyond that. There seems to be a fundamental air leak. it is often suggested to take a stiff binder book cover or similar and block off the air horn (accordion duct removed) while the engine is idling to try to stall it. if it still runs, you can often hear the point of the air leak under the plenum.

The linkage bracket cage, bolted to the side of the throttle body, COULD be bolted back on to the TB, such that it's in a slightly different position, which COULD necessitate the Min Idle adjustment.