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Discussion Starter #1 (Edited)
Hello Everyone,

I recently picked up a 2005 Black Cobalt as a commuter car. It was getting a bit expensive to dive my 2011 GMC Sierra 2500, $90 or more a week.

Anyways, the Cobalt is a base model, 5 speed, and has about 159k miles on it. It was idling rough when I bought it but I knew the codes going into it and had a feeling all I needed to do was clean the throttle body and and MAF. Did that, but wrong as I found out later. I removed the TB from the engine, moved the butterfly valve, cleaned it, put it all back together and then it started idling at 1650ish RPMs. Did a bunch of research and nothing seems to be able to bring the RPMs down to normal and I am not ready to get it reflashed. I did try something didn't read which helped a bit. I got it to idle at about 800 rmps for about an hour, disconnected the negative on the battery while it was running, then shut it off for a few hours and now it idles around 1350. I may try that again this weekend if time permits. Any other ideas would be appreciated.

I have 2 separate issues as well that I will post up in the appropriate sections!

I have already learned a good bit from you guys, so thanks for the great info!

- Matt
 

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Welcome to the forums!

If you haven't tried it, go through the throttle body relearn process (which I don't know off the top of my head since I haven't done it). That tends to help with improper idle RPMs.
 

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I tried that a few times, assuming you are talking about the 3 mins of idle, 1 min of car off (key out). Repeat as needed... That didn't work for very long. As soon as I would give the car gas, it would go back up to a high idle. I have even tried applying the parking break, putting it in 1st and slipping the clutch till the rpms get to 800 until it stays, then letting it idle there for about 30 mins.

The results I have read about that work the best, in order are: 1) get it reflashed 2) just drive it and it should continue to drop, but may take several hundred miles and several weeks, 3) replace throttle body with new throttle body 4) dont worry about it and drive.
 

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Just wanted to provide and update on the High Idle.

It seems that waiting it out worked the best. After I got the car to idle at normal idle rpms, I left it running for a while, about 45 mins. Then while it was running I disconnected the negative on the battery and shut off the car. After letting it sit several hours, I connected the battery and started it up. It was now idling at about 1300 rpms. After being frustrated with my results I just drove the car. The other day while at a red light, I decided to try and get the rpms down by applying the parking break, putting it in 1st and letting the clutch out, forcing the rpms down. With no expectations of it working permanently I didn't have much hope of the rpms staying down after driving. Anyways, I am happy to report that the cobalt is idling normally now!! I am pretty excited about that.

Now it doesn't seem to be idling as smooth as it could be. I am going to change the fuel filter and spark plugs soon to see if that helps.
 

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Splurge and order a coil pack from some place. It will cost about $25 and save your $500 is other problems.
Try rockauto as a starting point and a few of the gmpartsxxxxx dot com. And get the factory STOCK AC plugs.....they worked well for 150k miles....a new set should work for a while for you with little problems.
 
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