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  #1  
Unread 06-29-2010, 05:16 PM
loligator loligator is offline
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Default Replaced throttle position sensor and now have high idle

Hey all,

My girlfriend has a 98 Chevrolet Cavalier Z24 (2.4L). It started running real rough, idling very funny (the idle was all over the place, up and down, up and down), and then the check engine light finally came on. The code I got from it said the throttle positioning sensor had a low voltage reading. I've since replaced it and the idle isn't all over the place but it's not right either. Lets say I'm driving 55 down the highway and I'm coming up to a red light. Hit the brakes and the idle goes down as expected, but probably 9 times out of 10, it will stay at 1500 for about 10 seconds before dropping to where it's suppose to be. The OBD II scanner I have also now picks up a high idle code (but no longer the TPS low voltage code).

I followed the repair manual when I installed the sensor. They warn that improperly installing it could result in a high idle or other idling issues. The instructions said to slide the sensor onto the shaft, then rotate it counter clockwise until the bolt holes are properly aligned. I didn't have to turn the sensor at all... It was properly aligned when I slid it on the shaft. Should I have spun it 360 degrees counter clockwise? The instructions don't say to do this and there isn't really enough clearance to do so anyway. I even removed the sensor and reseated it thinking maybe I did something wrong but still the same result.

Although the car is drivable, I'd still like to get this resolved. Any ideas would be greatly appreciated.
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  #2  
Unread 06-30-2010, 11:11 PM
politeios politeios is offline
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You might try cleaning your IAC
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Chevrolet Cavalier Coupe, 2.2l | 3-speed automatic
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  #3  
Unread 07-01-2010, 09:26 AM
loligator loligator is offline
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How does one clean the valve? I read spraying it with WD40 works well but thought I'd double check.
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  #4  
Unread 07-02-2010, 07:23 AM
tommyleea tommyleea is offline
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Reading codes is a good feature, but remember that you are more than likely seeing the symptom, and not necessarily the cause. If the idle is high; for whatever reason, the TPS will naturally have an abnormal reading. If the engine is running rich or lean, the O2 sensor will have a high or low reading. That's what it does; senses oxygen. It sounds like your only problem is at idle, so as stated earlier, I would inspect and clean the IAC and its connector. Carb cleaner will clean the valve. Next, before I changed too many parts, I would take it to a shop, and have them narrow the problem down so you don't throw your money away. Cheers

TommyJ
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  #5  
Unread 07-02-2010, 10:41 AM
loligator loligator is offline
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Thanks for the reply Tommy. The TP sensor was definitely bad as the car was having other problems that were alleviated after I replaced it. I did remove the IAC valve and cleaned it up but it hasn't seemed to have help the problem. I'd much prefer to just take it to a shop but unfortunately I don't have the funding for that now. I'm not sure what I'm going to do with it... The main issue now is the strange idling, when it jumps from 1k to 2k and goes back and forth back and forth.
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  #6  
Unread 07-03-2010, 07:44 AM
tommyleea tommyleea is offline
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Quote:
Originally Posted by loligator View Post
Thanks for the reply Tommy. The TP sensor was definitely bad as the car was having other problems that were alleviated after I replaced it. I did remove the IAC valve and cleaned it up but it hasn't seemed to have help the problem. I'd much prefer to just take it to a shop but unfortunately I don't have the funding for that now. I'm not sure what I'm going to do with it... The main issue now is the strange idling, when it jumps from 1k to 2k and goes back and forth back and forth.
Check for any vacuum leaks. Check all your hoses. Did your TPS have resistance when you turned it, or was it free wheeling? Unplug your IAC with the engine running, and see if the RPM changes. What is your idle supposed to be set at? 1000 RPM seems kind of high to me. Cheers.

TommyJ
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  #7  
Unread 07-06-2010, 06:02 AM
loligator loligator is offline
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Quote:
Originally Posted by tommyleea View Post
Check for any vacuum leaks. Check all your hoses. Did your TPS have resistance when you turned it, or was it free wheeling? Unplug your IAC with the engine running, and see if the RPM changes. What is your idle supposed to be set at? 1000 RPM seems kind of high to me. Cheers.

TommyJ
idling speed should be around 650 to 700 I believe. As for resistance on the TPS, I'm not sure what you mean. I'll try unplugging the IAC valve when this thing starts acting up again. As strangely as this problem came on, it seems to have disappeared again. I guess time will tell.
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  #8  
Unread 07-06-2010, 06:24 AM
tommyleea tommyleea is offline
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Quote:
Originally Posted by loligator View Post
idling speed should be around 650 to 700 I believe. As for resistance on the TPS, I'm not sure what you mean. I'll try unplugging the IAC valve when this thing starts acting up again. As strangely as this problem came on, it seems to have disappeared again. I guess time will tell.
You can unplug it now, with it running good, and see what the result is. Let me know. Cheers..

TommyJ
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