1998 Chevy Astro Fuel Economy

Tiny
AA0BL
  • MEMBER
  • 1998 CHEVROLET ASTRO
  • 6 CYL
  • AWD
  • AUTOMATIC
  • 109,000 MILES
A service center recently replaced the intake manifold. Since then, mileage has dropped form 20 mpg to 11.5 mpg.
The service center has not been able to correct the problem, even though I have taken it back to them on 3 occasions since the replacement of the intake manifold.
I am not seeing any indicators to tell me that there is a problem with any of the systems.
What should I consider doing next? This has been a very dependable ride up until now.
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Sunday, August 30th, 2009 AT 12:13 PM

3 Replies

Tiny
IMPALASS
  • EXPERT
Hello -

Sometimes a bad IAT (Intake Air Temperature) sensor can cause this. You can do a couple of things.

Please go to Auto Zone (AZ) or O'Reilly's (OR) and for FREE they can pull the codes to the car. Most important: Once they check your codes, if they find something and you don't get it fixed and need to get back with us, please make sure you tell us exactly what the code was, number and all. Example, if the code was E0568 O2 Sensor bad. Then make sure you give us all of that. While there for FREE also they can bring their tester out and check your battery and alternator.

The problem is sometimes it can be defective but not enough to throw a code.

Check it out with an ohm meter.

Intake Air Temperature (IAT) Sensor
If an IAT sensor-related code is present, perform appropriate DTC test. See TESTS W/CODES article. An out-of-calibration sensor may not set a trouble code. Use following procedure to test calibration. Disconnect IAT sensor harness connector. Measure resistance between IAT sensor terminals. Sensor resistance should be as specified. See IAT SENSOR RESISTANCE VALUES table. Resistance should be high when air temperature is cold and drop as air temperature warms. With vehicle sitting overnight, IAT sensor and coolant sensor should have close to the same resistance reading.


http://www.2carpros.com/forum/automotive_pictures/248015_Chart_1.jpg



Also try cleaning your Mass Air Flow sensor with a circuit board electrical cleaner.

Check all of your vacuum hoses REALLY good to make sure they are not split and on correctly.
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Sunday, August 30th, 2009 AT 12:54 PM
Tiny
AA0BL
  • MEMBER
Thank you. I will share this information with my service center. They have been servicing my vehicles for the past 20 years, and have been very reliable, but this one seems to have them stumped.
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Sunday, August 30th, 2009 AT 11:05 PM
Tiny
IMPALASS
  • EXPERT
Hello -

That is great to hear that you have a reliable place to work on your vehicle.

Let us know what you find out and if we need to go farther we will.
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Monday, August 31st, 2009 AT 9:28 PM

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