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C. Walker, Jr.
C. Walker, Jr., Auto Mechanic
Category: Chevy
Satisfied Customers: 710
Experience:  Shop training and experience.
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I'm having rough idle after the engine warms up. I have done

Customer Question

I'm having rough idle after the engine warms up. I have done a lot of things to fix my 06 hhr 2.4l ecotec. I've replaced air filter, MAF sensor, intake and exhaust selenoids, spark plugs as well as cleaned the throttle body and a bottle of injector cleaner. Still after idling once it gets to operating temperature the rpms drop and it surges repeatedly. The tc light comes on and the check engine light flashes. Everytime I check the code it's p0300 Random multiple misfire. It's got me baffled. I've checked for vacuum leaks as well as cleaned g107 ground. I'm worried it's timing chain stretched or whorped head. Any suggestions?
JA: Have you seen the misfire code before? Has the car been stalling?
Customer: Not till I changed intake and exhaust selenoids then the idle problem began.
JA: What year is your Tc?
Customer: Tc?
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: I ever pretty much exhausted my level of expertise in was just curious if there is something I've over looked.....I've tried everything I stated before since the problem began
JA: Anything else you think the mechanic should know?
Customer: Not that I can think of
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Chevy Mechanic about your situation and then connect you two.
Submitted: 1 year ago.
Category: Chevy
Expert:  Lou P. replied 1 year ago.

Hello, so if i read your issue correctly, the engine did not misfire until the intake and exhaust solenoids were replaced?

Customer: replied 1 year ago.
I had codes p0011 which was the selenoid but while I was in there I changed both selenoids. Now with the bad selenoid the car ran like crap and idled rough as well as shifting hard. So I fixed the issue with shifting hard (selenoids ) but still have idle issue that's when I went with air filter, plugs throttle body cleaning, g107 ground change maf sensor injection cleaner. Still no fix in idle. The car is running the best it ever has off idle but once the idle miss fires the cel comes on and sometimes tc light and I runs like crap
Expert:  Lou P. replied 1 year ago.

ok , and the only code you get is the random cylinder misfire p0300?

have you sprayed the engine for vacuum leaks? also have you unplugged the mass air flow sensor and ran the engine to see if it would run better or worse?

Customer: replied 1 year ago.
I have visually inspected for vacuum leaks hose are tight and no visual defects. What should I spray them with? Also I replaced maf sensor and still no difference.
Expert:  Lou P. replied 1 year ago.

ok running without the mass air flow will tell a lot so try that as well, you spray around the intake and hoses with carb or brake cleaner to see if the rpms change, also when was the last time the oil was changed and what kind of oil was used?

Customer: replied 1 year ago.
Just curious but would a vacuum leak wait till the engine was hot before it showed itself
Customer: replied 1 year ago.
Oil was changed last week but I must confess my niece has been "borrowing" the car and I don't think she kept up with oil changes..... I will try those things and let you know what I find
Expert:  Lou P. replied 1 year ago.

depends , depends on where the leak is at, hard to explain thoroughly, when cold engines need more fuel then air and vice versa when hot but if the vacuum leak changed manifold pressure it will make the engine computer think the car was not at idle and supply more fuel, so many variables and scenarios lol, so yes it can , also can a failed temperature sensor, but lets take one step at a time to rule out.

Customer: replied 1 year ago.
Ok I sprayed for leaks and no change in rpms. With maf plugged in it idles ok untill the fan kicks on then tc light comes on and cel flashes and idle begins to surge up and down. I checked the codes and it showed p0300 Random misfire. I cleared the code and unplugged maf sensor and it idled ok with a slight drop in rpms when the fan kicks on but doesn't surge like it does when maf is plugged in. I checked the codes again and no p0300 but did get p0102mass or volume air flow a circuit input and p0113 intake air temperature sensor circuit high input. I'm assuming that's from unplugged maf.
Customer: replied 1 year ago.
I forgot to add with the maf unplugged the tc light comes on immediately and with it plugged in it doesn't come on till the surging begins
Expert:  Lou P. replied 1 year ago.

ok tc as in throttle control? or traction control?

is ac on or off, try with it off see if car runs ok, was ac charged recently?

Customer: replied 1 year ago.
Tc as in traction control. I haven't had ac on because I figured it would put more strain on the engine. To answer your question no the ac hasn't been charged recently it blows cold but I haven't been running it because of the issues. I did notice that the coolant temp is getting up to 217 before coolant cycles. It doesn't act up till the temp gets up to about 210 then at 217 when it cycles the tc light kicks on and idle surges up and down then cel blinks. Riding around town temps stay normal 185 to 194 and as long as it doesn't sit still at a light long and get hot it rides like a dream.
Customer: replied 1 year ago.
I've cut the car off when the tc light comes on before cel blinks and pull the codes all I get is p0300
Expert:  Lou P. replied 1 year ago.

ok let me opt out and see if another expert has some better ideas, sorry we could not come to a fast conclusion.

Customer: replied 1 year ago.
Ok thanks for the help anyhow
Expert:  Tim's Auto Repair replied 1 year ago.

Hi, My name is ***** ***** for the delay.

I will do my best to assist you.

the first thing i want you to try is a new ect sensor[engine coolant tempeture]..these can do this and not give a code for it,,with that being said and from the way you explain,i think your problem is the coil plugh boots[this is the rubber/plastic piece that gos over the spark plugs from the coils[works as the plug wire]..these are known to go bad and cause a major miss-fire

thanks

PLEASE COPY AND PASTE the link below to your browser, I have uploaded more info on this there please copy and paste the link below to your main browser[INTERNET EXPLORER or FIREFOX]

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https://www.dropbox.com/s/1fv62yhsuetn4eb/0621-hhr-P0300.doc?dl=0

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if the link doesn’t work that way, try it this way

thanks

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www.dropbox.com/s/1fv62yhsuetn4eb/0621-hhr-P0300.doc?dl=0

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If you are satisfied with my answer, Please Rate my answer by clicking the rating button so I can get credit for my work. I’m not always going to be giving you good news, so please don't let this stand in the way of you accepting my answer. .it does not cost you more money and we will still be able to communicate, ,.please understand, i can not see, hear or touch the vehicle and only know what you tell me. Bonuses and positive feedback are appreciated.. if you are not satisfied with my answer, please do not leave bad feed back ,i will gladly opt out and let another expert handle the question. .if i have sent any diagrams, please print them. .sometimes you may need to right click the image [,then save picture as]to save it to your computer so you can open it with your picture program...Please ask if you need more help

Customer: replied 1 year ago.
I will replace the ect this afternoon. I was wondering about a bad boot myself but it's not giving me a specific cylinder just a random misfire. I will let you know how it goes thanks.
Expert:  Tim's Auto Repair replied 1 year ago.

thanks

Customer: replied 1 year ago.
Ok I've changed ect sensor and boots still having the same issue.
Expert:  Tim's Auto Repair replied 1 year ago.

still only get the 300 code?

Customer: replied 1 year ago.
Yeah just the 300
Expert:  Tim's Auto Repair replied 1 year ago.

ok

stand by,i will opt out.perhaps one of the other guys mmay have a better idea of what is gong on here.

someone will be right with you

Expert:  C. Walker, Jr. replied 1 year ago.

Good evening, New expert here, have you done a compression test on the engine?

Customer: replied 1 year ago.
I haven't but just did it and the 2 outside cylinders are around 150 psi to 160 psi but the 2 inside cylinders are around 110 psi to 120psi.
Expert:  C. Walker, Jr. replied 1 year ago.

That is to low. I would do a wet test to determine if it is just a problem with the rings if it does not go up even with a little oil in the cylinder this would indicate you have something worse than just rings. Sometimes if the rings get build up of carbon you can run some seafoam through the engine and clean them up a bit. You can also run some Lucus engine oil stabilizer to help. But you will be looking at a engine service in the near future. You will continue to get the misfires and you can basically keep replacing the spark plugs on those 2 cylinders and keep driving it as long as it is a ring issue but it will never run right.

Customer: replied 1 year ago.
What's the typical cost of replacing the rings
Expert:  C. Walker, Jr. replied 1 year ago.

You are looking at a full engine service 18.6 hours in labor and 35 bucks for the rings.