Engine runs rough on cold startup after new spark plugs installed

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SwellSpy

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Re: 2012 LR4 v8 HSE Lux
I recently had a check engine light and the computer indicated I had some engine misfires although, at the time, the engine was running great.

To save some money, I decided to change the spark plugs myself. It was only after my very amateur installation I learned that I needed to "gap" the spark plugs, which I did not do.

Now, the old girl starts very rough. The RPM gauge jumps all over the place before idling and often it doesn't want to start at all until after a few tries. Once running, she runs great and has no issues. It's the cold starts that get her.

I took her to my local mechanic to diagnose and they said it was likely the fuel injectors or fuel pump, or both. They didn't have the tools to diagnose so they told me to go to the dealership.

Anyone else run into this issue and find a resolution? Does it sound like a fuel injector issue or fuel pump issue? I am suspect because other than a check engine light and the spark plug recommendation from the computer, she ran perfectly fine before I touched it.

Another thread I read said something about a potential air intake issue. I am a very amateur mechanic, so I'm wondering if I may have tampered with the air intake when I was taking stuff apart to get to the spark plugs? Thanks in advance.
 
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f1racer328

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What kind of plugs did you install? How did the old plugs look?
 

ktm525

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Yes what plugs (numbers)? If NGK doubtful they needed to be gapped. Likely you do not have a coil properly inserted or wired. Did you unplug each individual coil or did you pull then with wire attached? Did you apply some dielectric grease to each spark plug boot?
 

jlglr4

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Sounds like you had misfires that were made worse by the plug change - so normally I would agree with KTM and suspect a coil problem. But I am curious about this statement: “other than the check engine light and the spark plug recommendation from the computer.” What does that mean - did you have some kind of a code that said you had a bad plug? Did the mechanic pull any additional codes afterwards?
 

SwellSpy

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Thanks all.

What kind of plugs did you install? How did the old plugs look?
I installed the Bosch Double Iridium Spark Plug 96327 plugs, they were brand new. The old plugs did not look bad but the car was well over the recommended mileage.

Did you unplug each individual coil or did you pull then with wire attached?
I pulled them with the wire attached.

Did you apply some dielectric grease to each spark plug boot?
I did not. I learned about this after I installed them. Is this a necessity? If so, can you send me a resource link on how to apply it?

But I am curious about this statement: “other than the check engine light and the spark plug recommendation from the computer.” What does that mean - did you have some kind of a code that said you had a bad plug?
The codes I got before I installed the spark plugs (and went to the mechanic) were:
PO300 - random misfire detected
PO302,3,4,5,6,7- Cylinder 2,3,etc Misfire Detected
PO316 - Misfire Detected on Startup (First 1000 Revolutions)

Thanks, everyone.
 

ktm525

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I would start at the Bosch plugs. NGK or Denso iridiums. Is there a reason you went Bosch? Double check all coil connections and make sure coils clicked on and plugs are torques to plug manufacturers spec. You may have broken a coil wire by pulling the coils with the wiring loom attached. Since your errors are random and not directed at a certain bank or cylinder I would start with the plugs.
 

greiswig

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What’s Bn RPB gauge?

You mention your amateur skill level: there are a lot of different things that might be going wrong. You may have broken the conductor in the harness by pulling on the wire wrong, or maybe they really did need to be gapped properly. If the symptoms are the same as before but worse, I would lean toward the spark being the problem and have that diagnosed and maybe done at a shop that knows Rovers.
 

SwellSpy

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Thanks @ktm and @greiswig. I went Bosch bc that's what they had at the local parts store and they were OEM. I'll take another look at the coil connections, thanks.

I'll probably take it to a Rover shop, admittedly the shop that looked at it last time seems unequipped to work on foreign cars.

I'll post an update here once I figure what the issue is. I can't help but think it is something simple based on the before and after and the comments here. Fingers crossed on that.

Cheers
 

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