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Old 07-15-2014, 07:54 AM   #1
Project84
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Location: Florence, KY
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2009 AURA XR
Default ScanGuageII showing TPS at 15 at idle

I only use the car to commute to work and back so far, which is only 7 miles one way. I have 45 miles on this tank of gas so far and the dash MPG display is showing an average of 18.7mpg for this tank. My last tank only managed to get me 299 miles for an average of 22mpg - I attributed it to all the idling/maintenance I've been doing on the car and I'm hoping to pull down 24-25mpg on this current tank.

I started wondering about the throttle body - I cleaned it a few weeks back and had to do a "reset" on it afterwards. I probably have 200 miles on it since then, so IDK if it's still in "learning mode" or what.

I realize it's electronic, and I've never had a car with this feature. But all the cars I've ever used my SGII in have shown TPS at 0 during idle. This car is showing 17 at idle while coasting, and 15-16 at a stopped idle. Just wondering if that's normal. I'm assuming it is, since the RPM's are right at 750 at idle.

Just odd, I barely put my foot on the gas to accelerate and TPS goes 40-45.

Any input/help is much appreciated!

...
John
'09 Saturn Aura XR 2.4L
Previous - '01 SL1 daily driver and '96 SL2 auto 40+mpg hypermiler.

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Old 07-15-2014, 04:00 PM   #2
fdryer
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2003 L-Series 3.0L Sedan
Default Re: ScanGuageII showing TPS at 15 at idle

Well, unless you have service manual info to understand why throttle position percentages are used and the amount representing idle position, anyone can misinterpret reader displays. Since your idle is normal, the throttle position represented as a percentage is referenced to its closed position (0%), making this a normal number. Mixing apples and oranges can be misleading when using scangauge since your other Saturn's throttle is never fully closed yet the position displayed is zero. Since neither the pcm nor scangauge cannot command the throttle body to fully closed position and read the tps output, the pcm and scangauge use the initial tps output as zero position (when in reality the throttle blade is actually open). Electronics with drive by wire systems are more precise and since the electric throttle can be commanded automatically to fully closed position, the ecm can use this position as true zero for calibration and any other throttle position is based on this initial reference position. EFI systems requires a little in-depth research to appreciate what goes on.

The following is a reprint for L300's using similar electric throttle bodies (throttle actuator);

Throttle Body Assembly

The throttle assembly contains the following components:
  • The throttle blade
  • The throttle actuator motor
  • The throttle position (TP) sensor 1 and 2
The throttle body functions similar to a conventional throttle body with the following exceptions:
  • An electric motor opens and closes the throttle valve.
  • The throttle blade is spring loaded in both directions and the default position is slightly open.
  • There are 2 individual TP sensors within the throttle body assembly.
The TP sensors are used to determine the throttle plate angle. The TP sensors provide the ECM with a signal voltage proportional to throttle plate movement. Both TP sensor signal voltages are low at closed throttle and increase as the throttle opens.

Modes of Operation

Normal Mode
During the operation of the TAC system, several modes or functions are considered normal. The following modes may be entered during normal operation:
  • Minimum pedal value--At key-up the ECM updates the learned minimum pedal value.
  • Minimum TP values--30 seconds after key-up the ECM updates the learned minimum TP value. In order to learn the minimum TP value, the throttle blade is moved to the closed position.
  • Ice break mode--If the throttle is not able to reach a predetermined minimum throttle position, the ice break mode is entered. During the ice break mode, the ECM commands the maximum pulse width several times to the throttle actuator motor in the closing direction.
  • Battery saver mode--After a predetermined time without engine RPM, the ECM commands the battery saver mode. During the battery saver mode, the TAC module removes the voltage from the motor control circuits, which removes the current draw used to maintain the idle position and allows the throttle to return to the spring loaded default position.

Once the throttle idle relearn is performed, its done. No break-in period.

...
VCX NANO

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Old 07-16-2014, 07:58 AM   #3
Project84
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2009 AURA XR
Default Re: ScanGuageII showing TPS at 15 at idle

Thanks fdryer - makes sense that SGII isn't reporting TPS at 0 now that I let it sink in that it's an electronic TB and cannot possibly run at 0 or a true closed position.

Also - I was kinda on the right track when I said my idle is correct at 750, if that's fine then I'd imagine TPS could report any number so long as it still functioned correctly, and all would be in harmony.

I'm going to hook up a vacuum gauge to the car and see how tight things are. Maybe I'll use that as a real-time display for improving my fuel economy.

...
John
'09 Saturn Aura XR 2.4L
Previous - '01 SL1 daily driver and '96 SL2 auto 40+mpg hypermiler.

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