1999 Toyota Camry Engine slows or speeds up at highway spee

1999 TOYOTA CAMRY
244,500 MILES • 6 CYL • FWD • AUTOMATIC
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BENNY SANDERS
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While driving 55,60,65 mph engine will start to slow down and sometimes even speed up some. I have replaced wires,plugs.air filter,fuel pump and screen. The egr valve ports are clean-even blocked the valve port but no change. IAC valve was replaced one year ago due to stalling at idle. Engine idle is fine as is excelleration to any speed with no miss,and no trouble codes. Also cleaned the throttle body. Also replaced boots under coils (3).
Jan 12, 2008 at 6:19 PM
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FLEXY5
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When it slows down is it a gradual reduction in speed or does it just fall on it's face? I don't know a whole lot about Toyota's but we'll see if we can diagnose by symptom.
Jan 12, 2008 at 8:31 PM
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BENNY SANDERS
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[quote:c341681321="flexy5"]When it slows down is it a gradual reduction in speed or does it just fall on it's face? I don't know a whole lot about Toyota's but we'll see if we can diagnose by symptom.[/quote:c341681321] it will suddenly start to decrease speed and the TPS and MAS readinds decrease as if you are letting off the gas. If you give a little gas it comes right back up-even may speed up on its own 5mph
Jan 12, 2008 at 9:03 PM
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FLEXY5
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I would have to wonder then about the TPS. If (in a certain range of throttle) the TPS shorts out, the computer would tell the computer to lessen the amount of fuel going through the injectors. As the engine bogs down, MAS would also decrease as the engine is now running at a lesser RPM. If you have access to a diagnostic computer, try monitoring TPS without having the engine running. Perform a sweep of all TPS ranges VERY SLOWLY and see if there is a point at which the TPS signal either remains the same or drops off.
Jan 12, 2008 at 9:20 PM
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BENNY SANDERS
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[quote:6b01e34954="flexy5"]I would have to wonder then about the TPS. If (in a certain range of throttle) the TPS shorts out, the computer would tell the computer to lessen the amount of fuel going through the injectors. As the engine bogs down, MAS would also decrease as the engine is now running at a lesser RPM. If you have access to a diagnostic computer, try monitoring TPS without having the engine running. Perform a sweep of all TPS ranges VERY SLOWLY and see if there is a point at which the TPS signal either remains the same or drops off.[/quote:6b01e34954] I REPLACED THE tps AND NO CHANGE-the sweep looks ok-can the mass airlow sensor cause this?
Jan 12, 2008 at 9:41 PM