For about 3 years now I have been living with a rough idle while in gear issue making it very annoying to stop at red lights or sitting in traffif. Since the car is a 2007 hhr with 260,000+ km on it I just resigned to living with it and only periodically looking into the issue. Since there were no check engine lights on i figure maybe the old girl was getting tired. But every once in a while I would swap out some parts just out of curioisity. After changing a miriad of parts(mostly with parts from scrap yard) like MAF/MAP sensors, O2 sensors I just gave up.
Well last week I was cleaning out My scrap yard tool box and found an evap purge valve that I had taken off a car at the scrap yard. So I figured what the hell Ill pop it in and see what happens.
The result was a 95% improvement in the idle. Its no longer annoying to stop at red lights or in traffic...I've been monitoring the idle closely at every red light / stop sign for about a week and its consistantly 95 percent perfect non shakey idle @ -+ 650rpm.
Just funny that no check engine light would come on with this part failing.

 

Good tip - did you throw a code reader on it even tho' the CEL never came on? Sometimes there are pending codes etc. that can affect the running, without lighting up the CEL.

 

A good place to start when others post similar symptoms.

 

Yes I checked for codes. I've only had 1 check engine light in the 9+ years of owning the car and that was the evap system solenoid under the rear of the car. I changed that about 1 year ago(1 day after the light came on). The plastic housing around the solenoid was cracked.. Changed it out cleared the code and never a check engine light again.
It's just so nice to relax at red lights now. I shut off all fans turn down the radio and it feels like the engine isn't even running....

 

Might give that a try on my car. Can be at stop light and car would try to surge forward and rpm's would go up and down. Give it gas and it goes away. I've checked the codes and no pending codes for that.

 

Forgot to mention I also changed motor mounts at the very start of the problem as well without success. The only thing that worked (knock on wood) was the evap purge valve.. The one in the engine bay..

 

You my friend, are a genius. For anyone with this annoying issue, this fix is spot on. Doesn't show up with a code or anything, so I'm sure the dealership would be clueless.
The symptoms are rpms getting hung up on the way down, then a rumble at idle, like a subway train is passing under you. Now the idle is smooth, and rpms come down quicker and smoother...nice
thanks for the post

As an awesome consequential benefit, there was an immediate change under acceleration. It is now smoother and responsive, both in sound and feel...wow who would thought that this small item would make such a big difference. With only 72k it just goes to show you that this part could not operate properly, and create this annoying problem.

Anyone know what fails on this thing or what causes it. My first hunch was maybe extreme high humidity because mine spent its first 9 years in Florida.

Anyway just want everyone know if you have this problem this part seems like the first choice to maks. Its $47