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.



Try unhooking the negative battery cable for about a min then hook it back up and see how it runs?

Saturntech9
Dec 12, 2012.
Well I'm convinced the issue I s the pcv tube. Do you remember that tube I replaced three months ago? It looks like the hose I got from autozone. So I've ordered the hose from a gm parts store. Will let you know how it turns out.

Tiny
Dlvaughn1963
Dec 12, 2012.
Whats wrong with the tube is it bad again?

Saturntech9
Dec 12, 2012.
It's not holding a seal where it goes into the valve cover

Tiny
Dlvaughn1963
Dec 12, 2012.
Have you tried putting on a hose clamp to see if it takes care of the problem?

Saturntech9
Dec 13, 2012.
Can't be clamped. I think the aftermarket hoses do not have the right dimensions for the hole the tube "t" goes in. The oem plug part is rubber and has a better fit. The aftermarket hose has a plastic "finned" plug that does not offer a tight enough fit for the hole, so there must be a grommet needed if you use the aftermarket hose. The problem with trying this, is you would have to take the throttle body off, and remove a clamp to do all this. Then I'd need a gasket and other things. I've ordered another hose, but this one is supposed to be oem. I will see when it gets here on Monday.

Tiny
Dlvaughn1963
Dec 14, 2012.
Sounds good keep me posted.

Saturntech9
Dec 15, 2012.
Well replaced the line and as always the initial start sounds good, then the random misfiring starts up. It seems that anytime something is replaced, it changes but not really fixed. It seem that when I replace a part, the engine goes thru a high rev that seem to cycle for about four accelerations. I attribute this to the engine computer relearning for idle mixtures. Of course when the engine goes though the rough idle cycles with the misfires, the intake air sounds like its being blocked or rerouted. I'm wondering if my mass airflow sensor is bad. Cause when I unplug it and let the engine run, it seems to settle to normal. I did get to replace the coolant temp sensor but that has not changed anything. I'm almost running out of options.

Tiny
Dlvaughn1963
Dec 18, 2012.
Try lightly tapping on the mass air flow sensor with a screw driver handle see if it runs any different?You could also try cleaning the mass air flow sensor with some mass air flow sensor cleaner.

Saturntech9
Dec 18, 2012.
I unplugged and plugged the sensor, ran engine no change. Cleaned the MAF sensor last month, got no appreciable difference in performance. I'm not ruling out some sort of either gasket leak or possibly maybe even really bad fuel injector clogging. However I have read it will cost me quite a bit for gasket work, and I'm not gonna spend this much money on it. Ive only known about this misfire condition until I fixed the high idle issue. I'm at a loss now. The only part I have not changed is the ICM and Ive read that this component is either good or bad.

Tiny
Dlvaughn1963
Dec 18, 2012.
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