# Rough Idle-New Spark Plugs, Ignition Coil, & Tune did not fix....



## TetraHC (May 13, 2020)

Hey all, looking for some additional feedback for my 2015 Chevy Cruze LS 1.8.
-This car has given me a handful of stress. I’ve been going through the motions of replacing intake & exhaust manifolds. Swapped out my ignition coil with an OEM, I’m also running NGK spark plugs. On top of parts I’ve purchased a trifecta tune to even out the air/fuel ratio. All this, & my Chevy is still running pretty rough when idling. I’m convinced it’s a misfire, pretty bad one at that. What else can I check to fix the issue? I’m considering doing a compression test.


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## rob.lafady (Dec 25, 2016)

I had a bad idle issue I finally took to the dealer to sort out, they say they found broken wiring under the fuel tank, all I know is it runs a whole lot better!

Sent from my moto g(7) using Tapatalk


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## JLL (Sep 12, 2017)

Have you scanned for codes?


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## TetraHC (May 13, 2020)

Yes. There were no codes with my OB2 or Trifecta program.


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## JLL (Sep 12, 2017)

Hmm. Normally misfires leave codes of some sort. You can try a compression test. OR It could be your engine mount(s) are worn out causing the engine to transmit vibrations to the body of the car causing symptoms that mimic a misfire?


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## TetraHC (May 13, 2020)

I'm convinced its a misfire because the car won't drive well. It "Coughs" & is very sluggish, barely made it up my hill to my garage. When idling, it hums at first and then the RPM needle starts to bounce around 1k


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## Shroomie (Jan 16, 2017)

Your car has a breathing problem and since it's worse at idle.. pcv issue, exhaust restrictions, vacuum leak


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## TetraHC (May 13, 2020)

UPDATE**
I took my car to the dealership to have them try and fix the issue. They fried an ignition coil & spark plug so I ended up paying for those, we removed the tune in my car & it ran okay stock for about 2 weeks before I started having a very rough idle & poor jerky acceleration. I was able to get some codes while getting my car home.
P0301
U0100
P0137
P2301
P2270

Any ideas guys?


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## obermd (Mar 3, 2012)

TetraHC said:


> UPDATE**
> I took my car to the dealership to have them try and fix the issue. They fried an ignition coil & spark plug so I ended up paying for those, we removed the tune in my car & it ran okay stock for about 2 weeks before I started having a very rough idle & poor jerky acceleration. I was able to get some codes while getting my car home.
> P0301
> U0100
> ...


You have an electrical problem. 

Cylinder 1 misfire
Communications error
O2 sensor low voltage
Ignition coil voltage
O2 sensor

Has your car had the negative battery cable replaced yet? If not, I'd start there. Special Coverage #14311: Negative Battery Cable. Once this is done, clear the codes and leave the stock tune on to see what happens.


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## -loki- (Dec 13, 2019)

A bad ground could do that all of the above. It makes a good bit of difference.


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## TetraHC (May 13, 2020)

I never considered the negative battery cable. I figured electrical as well & bought a new preprogrammrd ECU that will be here in a few days, will update with results.

If the ECU doesnt help the ground cable will be my next bet.


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## Blasirl (Mar 31, 2015)

I would have said spark blowout to your initial post. What is your plug gap? The 1.8 untuned should be .028.


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## TetraHC (May 13, 2020)

UPDATE: 
-Plugs were installed by the dealer, i double checked the gap & they all check out.

-New ECU didnt fix my issue🤬 & i melted another ignition coil. Spark plugs looked fine & the coil melted after running smooth for 3min. Idfk

--My next move is to sell this POS, Im done! Sorry i couldnt come to a solution for you guys with the same issue. ✌🏾


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## TetraHC (May 13, 2020)

UPDATE:
-I didn't sell her quite yet. I replaced my *VALVE COVER GASKET* & have had no issues at idle. No codes, no bouncing needles, no burnt up coil packs. Ill be taking it for a drive in a bit but for anyone reading this discussion, check your valve cover gaskets FIRST! It's simple & I've wasted a couple grand when I just needed a $30 gasket.


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## Shroomie (Jan 16, 2017)

Shroomie said:


> Your car has a breathing problem and since it's worse at idle.. pcv issue, exhaust restrictions, vacuum leak





TetraHC said:


> UPDATE:
> -I didn't sell her quite yet😄 I replaced my *VALVE COVER GASKET* & have had no issues at idle. No codes, no bouncing needles, no burnt up coil packs. Ill be taking it for a drive in a bit but for anyone reading this discussion, check your valve cover gaskets FIRST! It's simple & I've wasted a couple grand when I just needed a $30 gasket.😄


😉


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## JLL (Sep 12, 2017)

TetraHC said:


> UPDATE:
> -I didn't sell her quite yet😄 I replaced my *VALVE COVER GASKET* & have had no issues at idle. No codes, no bouncing needles, no burnt up coil packs. Ill be taking it for a drive in a bit but for anyone reading this discussion, check your valve cover gaskets FIRST! It's simple & I've wasted a couple grand when I just needed a $30 gasket.😄


Next time don't condemn the car so quickly. I'm guessing you paid good money for it. PATIENCE and GOOD DIAGNOSTICS go a long way. Especially with a Cruze.


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