1999 Toyota Camry Engine slows or speeds up at highway spee

BENNY SANDERS

MEMBER
1999 TOYOTA CAMRY
6 CYL
FWD
AUTOMATIC
244,500 MILES

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).

4 Replies

FLEXY5

MECHANIC
512 POSTS

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.

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Saturday, January 12th, 2008 AT 8:31 PM

BENNY SANDERS

MEMBER
3 POSTS

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

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Saturday, January 12th, 2008 AT 9:03 PM

FLEXY5

MECHANIC
512 POSTS

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.

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Saturday, January 12th, 2008 AT 9:20 PM

BENNY SANDERS