I am in dire need of help. My hhr has 75,000 miles on it and is running rough at idle. So far I have replaced the throttle body, intake, maf sensor, coils, spark plugs, vvt solenoids, new battery, and much more. Still the same issues it runs fine under throttle but has slight misfire across all cylinders at idle, not enough to make it stumble or die out but rpm bounces around and it shakes. One second it will run okay then it freaks out. I have tried doing the idle relearn and nothing changes. The only weird thing is the coolant temp sensor bounces so I have ordered one of those but I cannot imagine that would cause the vehicle to run so poorly. Any help at all is appreciated I’m am so lost and fed up at this point.

 

Welcome to the site. You replaced parts, my question would be on what basis did you decide to do that?
what brand parts did you use? I’m asking to get an idea of your cars situation. Is P0300 the only code?
what spark plugs did you install?
how old is your air filter?
Have you checked your timing chain?
Have you checked the timing chain front guide?
as those wear out or the front guide bolts loosen up , timing is effected, but usually sets other codes.
let us know.

 

P0300 is the only code and it doesn’t even show up all the time. Originally when I got the car it ran semi poorly so I thought a quick tune up would correct it so that is when I replaced spark plugs and coils. I used Ngk iridium’s for plugs and ngk branded coils also. I continued driving it and I got a maf sensor code so I replaced it with a cheap one off rock auto and the car ran worse so I went to the parts store and got a gm sensor which seemed to help and cleared the code. Then I got a throttle position sensor. Pulled off the throttle body and cleaned it which turned into it running like crap. This was where a lot of my problems got worse. I did the relearn multiple times but it never idled high just bounces around between 600-800rpm at idle very sporadically. I then purchased a bosh throttle body because I saw forums recommended that but it did nothing to remedy my issues. The car then sat for about a year or so because I had other vehicles. Now since I’ve started to dig back into it. I put brand new plugs on it again (ngk iridium) new vvt solenoids new air filter new battery and still no avail. Checked compression and got 210 across all 4 cylinders. I tried advancing and retarding timing through my scanner and it got way worse both ways so I figured my timing was good. Could the idle relearn be a cause of it running horribly? Everything I’ve seen was people saying it idles high when it needs a relearn.

 

Ok, the NGK plugs are known to not play nice with the Ecotec engine, install a set of AC Delco 41-103 iridium plugs. Rock Auto is usually the best source both price and authentic parts.
Don’t try adjusting anything else with a scanner.

 

Okay will do. I’m going to pick up a coolant temp sensor also since it seems that the idling follows the sensor. My coolant sensor is bouncing around when cold from 100°f-200°f and the idle seems to bounce every-time the sensor does. Thank you I will keep you updated.

 

Those temperatures are telling me that the thermostat might be faulty. It should open at 180 F
after market tstats have this issue also.
I’ve determined that AC Delco 131-158 180 F thermostats work and last a long time. You fluctuation could be air in the system, burp the coolant first, cause that’s free ,

https://www.chevyhhr.net/forums/how-...-system-60614/

 

It’s 32° out where I’m at right now and as soon as I start it the temp sensor does will bounce. I will replace the thermostat too just to be safe.

 

Take the valve cover off and look at the timing chain; any slack between the the sprockets is bad.

 

A broken front chain guide is common.