99 Mailbu LS 3.1Intermittent Issues
426Cammin
05-10-2010, 03:20 PM
Hello all- experiencing starting issues, down-shift issues, and chugging upon takeoff (all intermittent).
Brief History: auto is family-owned since original purchase. Regular tune ups throughout (oil,oil filter,fuel filter, air filter, plugs,wires,belts, etc.). No trouble codes when these issues occur. Have tried gas additives, higher grades of gas, and several auto repair shops have been unable to correct/detect issues. Checked ground straps, vacuum hoses, fuses, and other simple items. Any help is greatly appreciated.
Issues breakdown:
1. Starting issues are very intermittent. Engine will turn over a few rotations then sputter to a stop. Will usually start right up with no issues during the next attempt directly following the first failed start. Higher Outside temp seems to be a determining factor.
2.Down-shift issues usually experienced when extra power needed (slight inclines, normal on-ramp acceleration, etc.). Down-shifts occur normally if depressing the pedal for sudden speed changes such as pulling out into busy traffic. The best description would be to think of the transmission rapidly changing between the gears back and forth for a few seconds. After the transmission finally gears down the car drives normally.
3.Take-off issues experieced during take off from a stop. Generally the issue appears to feel as if the engine is returning to idle, even though the gas peddle is depressed. Not to say that the engine dies, just a complete lack of power. Condition lasts one second and then power returns with a surge back to normal.
Brief History: auto is family-owned since original purchase. Regular tune ups throughout (oil,oil filter,fuel filter, air filter, plugs,wires,belts, etc.). No trouble codes when these issues occur. Have tried gas additives, higher grades of gas, and several auto repair shops have been unable to correct/detect issues. Checked ground straps, vacuum hoses, fuses, and other simple items. Any help is greatly appreciated.
Issues breakdown:
1. Starting issues are very intermittent. Engine will turn over a few rotations then sputter to a stop. Will usually start right up with no issues during the next attempt directly following the first failed start. Higher Outside temp seems to be a determining factor.
2.Down-shift issues usually experienced when extra power needed (slight inclines, normal on-ramp acceleration, etc.). Down-shifts occur normally if depressing the pedal for sudden speed changes such as pulling out into busy traffic. The best description would be to think of the transmission rapidly changing between the gears back and forth for a few seconds. After the transmission finally gears down the car drives normally.
3.Take-off issues experieced during take off from a stop. Generally the issue appears to feel as if the engine is returning to idle, even though the gas peddle is depressed. Not to say that the engine dies, just a complete lack of power. Condition lasts one second and then power returns with a surge back to normal.
serge_saati
05-10-2010, 04:02 PM
1) Starting: It could be a bad fuel pump, IAC valve, TPS, CKP sensor, CMP sensor, TPS sensor... Check engine light on?
2)Transmission: I think it's a bad TPS (throttle position sensor).
In your malibu, the transmission is controlled by a computer (PCM). If it thinks that you press too much the pedal, it downshifts. It's not a transmission problem if it happens only when you press the gas. How much times the gear change?
3) Take-off: It seems it's the TPS again. Cause when you press the gas, it doesn't detect it. The more you press, the more you add air w/o fuel, so it stalls. But it could be also a bad CKP, CMP, fuel pump.
But I thing your problem is a bad TPS. You can check it with a voltmeter by pressing the gas and monitor voltage on pin 2 (I think) of the connector. It should change from 0.9V to 5V. Connector must be connected during test (plug a small wire) and key must be to ON.
2)Transmission: I think it's a bad TPS (throttle position sensor).
In your malibu, the transmission is controlled by a computer (PCM). If it thinks that you press too much the pedal, it downshifts. It's not a transmission problem if it happens only when you press the gas. How much times the gear change?
3) Take-off: It seems it's the TPS again. Cause when you press the gas, it doesn't detect it. The more you press, the more you add air w/o fuel, so it stalls. But it could be also a bad CKP, CMP, fuel pump.
But I thing your problem is a bad TPS. You can check it with a voltmeter by pressing the gas and monitor voltage on pin 2 (I think) of the connector. It should change from 0.9V to 5V. Connector must be connected during test (plug a small wire) and key must be to ON.
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