Mechanics

HIGH IDLE ISSUE AND INTERMITTANT SHIFTING CAUSE IAC, TPS?

1999 Buick Century • 170,000 miles

Hello, I have a 99 Buick Century and recently I have experienced very high idle speeds and erratic shifting issues. I have cleaned the IAC valve, and did notice my throttle body was rather dirty on the inside. I had cleaned the throttle body with a cleaner, cleaned the IAC, and started the car. The idle was still high. I disconnected the IAC, the TPS, the air box sensor, the sensor on the air intake tube and the EGR sensor, I thought the car should have shuddered or something, so it ran high still. I connected all the sensors back, started the car and still high. My next thought is to disconnect the IAC alone, then the TPS alone. Is there anything I am missing? I have seen others with the same problem, but have not seen any sort of resolution. I thank you for your assistance.
Dennis
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Dlvaughn1963
September 24, 2012.




Will let you know definitely tomorrow. The PVC connector end looks like a plug boot cover that was put at the end of the tube. It also causes a whistling sound I think the boot that was used I too soft and causes the "cap" to collapse hense the horrible sound in the engine compartment.

Tiny
Dlvaughn1963
Sep 26, 2012.
That sounds like a good start keep me posted.

Saturntech9
Sep 26, 2012.
Replaced PVC tube, idle is much better. Computer must still be learning fuel mixtures and shifting is much better with some sluggishness. The old hose was loose on the vac connector from the vap solenoid. Will see how things work out after a few trips. I do still wonder about the IAC. The maintenance manual shows the removed position of the actuator so ill look into that next b

Tiny
Dlvaughn1963
Sep 27, 2012.
Try taking the negative battery cable off for about a min then put it back on and see how it works then.

Saturntech9
Sep 27, 2012.
Codes cleared still high. Will look at possible bad IAC

Tiny
Dlvaughn1963
Sep 27, 2012.
Have we looked for more vacuum leaks?What about the coolant temp sensor have. We looked at that yet?

Saturntech9
Sep 27, 2012.
Coolant temp is relative to engine performance. The temp at the moment never goes over half way

Tiny
Dlvaughn1963
Sep 28, 2012.
I have seen cars with no symptoms of overheating etc with a failing coolant temp sensor causing a high idle.

Saturntech9
Sep 28, 2012.
Ok will look at that next

Tiny
Dlvaughn1963
Sep 28, 2012.
The codes did clear when I disconnected battery but did come back. I suspect the bank1 o2 is still bad cause the fuse is again blown. This o2sensor is not easy to get to unless I pull the ignition control module and coils.
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Tiny
Dlvaughn1963
Sep 28, 2012.

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