'95 Grand Am

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Old 10-02-05, 01:43 PM
debracurtis
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'95 Grand Am

My son's '95 Pontiac Grand Am hesitates and acts like it wants to stall when driving at a consistant speed. Readings from throttle position sensor says there's not a problem with the senosr. This problem is driving us crazy. Can't seem to find any reason for it. Any help would be appreciated.
 
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Old 10-02-05, 07:09 PM
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Check for cracked/dry rotted/hard/broken vacuum lines. Small cracks in one line may not leak much, but small cracks in many lines cumulatively can cause major running problems.

Check other sensors: MAP sensor (Manifold Absolute Pressure) - Sometimes located on a bracket on the back of the engine or on the firewall. It's rectangular with one connector and one vacuum line. Controls fuel flow by sensing how much vacuum is in your intake manifold. Also senses higher altitudes and adjusts fuel/air ratios to compensate.

Oxygen sensor: Located in the exhaust manifold or in the exhaust pipe somewhere upstream of the catalytic converter. Some vehicles have a second sensor downstream of the catalytic converter. It generates a small voltage based on the amount of oxygen in the exhaust. Too much oxygen, the computer sends commands to increase fuel. Too little oxygen. the computer dials back on fuel. Test by reading with an analog voltmeter on a low voltage scale. Voltage is typically less than one volt and fluctuates up and down while idling. If the voltage is zero or a constant, fixed value, it's bad. Oxygen sensors often begin to crap out at around 30,000 miles. Don't touch the new sensor or get anything on it when installing, especially oil or grease. Exhaust manifold leaks can cause this sensor to read wrong when decelerating. Depending on where the leak is, air can be sucked in during deceleration and the oxygen sensor reads massive amounts of oxygen and really ramps up fuel delivery to compensate.

If the vehicle is equipped with a mass airflow (MAF) sensor (which I doubt) in the intake tube, tap it lightly with a screwdriver handle. If the engine immediately stalls or runs rough, the MAF sensor is bad. I don't think they were used much after the 80s because they were very problematic.
 
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Old 10-02-05, 07:48 PM
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Have you tuned it up?
 
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