High idle issue and intermittent shifting cause IAC, TPS?

Tiny
DLVAUGHN1963
  • 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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Monday, September 24th, 2012 AT 8:55 PM

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Tiny
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The tps can cause a high idle and a hard shift. Did you clear codes after plugging everything back in?

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Monday, September 24th, 2012 AT 8:59 PM
Tiny
DLVAUGHN1963
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I have not cleared the codes yet. I will have to go to Autozone to have them cleared. I also found the fuse for the O2 sensor was blown too. Might be possible I have bad sensors

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Monday, September 24th, 2012 AT 9:03 PM
Tiny
DLVAUGHN1963
  • MEMBER

If the codes are not cleared will it still have an effect on the idle speed? The check engine light seems to come on and go off intermittently

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Monday, September 24th, 2012 AT 9:04 PM
Tiny
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The blown fuse might have just been a shorted wire to the exhaust etc?Clear the codes and see which ones come back?Let me know the exact code numbers not code descriptions.

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Monday, September 24th, 2012 AT 9:06 PM
Tiny
DLVAUGHN1963
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Ok

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Monday, September 24th, 2012 AT 9:08 PM
Tiny
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Keep me posted.

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Monday, September 24th, 2012 AT 10:55 PM
Tiny
DLVAUGHN1963
  • MEMBER

Codes: p0134, p1635, p0401, p0101, p0108
To negate most of these prior to these codes the only one
I knew was probable was the O2 sensor code due to finding a blown
Fuse in the engine elect panel. I had disconnected every electrical
Connector on or around the top of the engine near the throttle body (map sensor, tps, iac, egr). A total of 5 connectors to see if there would be a change in performance and there was none. The one thing I have ordered is the PVC line assy because its bad. Won't tell you what the previous owner used. Would this line from the evap canister to the PVC cause this problem or do I have issues with the iac or tps? The iac was cleaned with no change less its internally shorted.

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Wednesday, September 26th, 2012 AT 3:01 PM
Tiny
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So the codes you listed are the ones that came back after you cleared them after plugging everything back in?Also you have a tee off the pcv hose that feeds vacuum to the evap canister purge solenoid?If that hose is leaking that would cause high idle etc. It shouldnt go directly to the charcoal canister or that will cause a problem also the vacuum flow to the canister is controled by the solenoid. Make sure the solenoid isnt stuck open?

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Wednesday, September 26th, 2012 AT 3:32 PM
Tiny
DLVAUGHN1963
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I cleared the codes today. I've ordered the evap/PVC hose an it should arrive tomorrow. So I'll know what happens. That hose caused my problem? Guess ill see tomorrow.

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Wednesday, September 26th, 2012 AT 6:44 PM
Tiny
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If its leaking vacuum it can cause a high idle etc.

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Wednesday, September 26th, 2012 AT 8:18 PM
Tiny
DLVAUGHN1963
  • MEMBER

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.

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Wednesday, September 26th, 2012 AT 8:26 PM
Tiny
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That sounds like a good start keep me posted.

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Wednesday, September 26th, 2012 AT 8:39 PM
Tiny
DLVAUGHN1963
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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

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Thursday, September 27th, 2012 AT 5:46 PM
Tiny
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Try taking the negative battery cable off for about a min then put it back on and see how it works then.

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Thursday, September 27th, 2012 AT 6:03 PM
Tiny
DLVAUGHN1963
  • MEMBER

Codes cleared still high. Will look at possible bad IAC

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Thursday, September 27th, 2012 AT 10:49 PM
Tiny
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Have we looked for more vacuum leaks?What about the coolant temp sensor have. We looked at that yet?

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Thursday, September 27th, 2012 AT 11:07 PM
Tiny
DLVAUGHN1963
  • MEMBER

Coolant temp is relative to engine performance. The temp at the moment never goes over half way

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Friday, September 28th, 2012 AT 12:23 AM
Tiny
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I have seen cars with no symptoms of overheating etc with a failing coolant temp sensor causing a high idle.

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Friday, September 28th, 2012 AT 1:19 AM
Tiny
DLVAUGHN1963
  • MEMBER

Ok will look at that next

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Friday, September 28th, 2012 AT 1:41 AM
Tiny
DLVAUGHN1963
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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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Friday, September 28th, 2012 AT 1:43 AM

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