Back in Feb, had mechanic replace the starter motor as there were intermittent starting problems. That fix worked.

This is my wife's car. Fast forward a couple months and she says that she noticed the car wasn't as peppy as it used to be. So, I cleaned the MAF and the throttle body. No changes.

After a road trip, I also noticed that we lose about 2mpg on fuel efficiency. And the acceleration from 40mph and up is more hesitant. So, not as"peppy" as it was before.

I bring it back up to the mechanic. He runs diagnostic and says there's a p0330 code. Knock sensor. But no CE light. And he says that shouldn't cause the issues.

I note that it's in the same area as where he changed the starter motor. He then says it wouldn't be related, but he could change it at my cost.

So two questions.

1. Could it be that his work on the starter did something to the KS and he should cover the replacement cost?

2. If I decide to do it myself, doable? I've seen some videos of taking off the manifold doesn't seem too bad. I do have some wrench time on cars. I didn't change the starter myself because the mechanic gave me a good deal to replace it.

Thanks for your insights.

How many miles are on our QX? When mine felt less peppy it was an easy plug change. Years later, started having an issue with hesitation and rpm surge around 25-30mph, found a few of my coils were going bad. Bought a new OEM set of coils and this vehicle feels like day one again. Went on a 3200 mile road trip for vacation this summer and averaged 19-20mpg and she ran smooth. I have 131K miles on my beast.

Had little over 100k miles. There's a code for the knock sensor. P0333. Although no check engine light. Interesting that the dealer never checked for it even after telling them of the loss of power. They checked and replaced the battery.

Anyway, ordering two new knock sensors and spark plugs to replace. May replace the coils too.

Start with that knock sensor since the dealer pulled a P0333 code. But with 100k miles, I would replace the plugs to the OEM plug and just inspect the coils. Remove the coil boot and make sure you don's see a milky residue coming from the coil to the spring. Should be nice and dry. OEM coils run about $400 for the set on rockauto just in case you go that route. Good luck man, keep us updated on your fix

TL:DR
Knock sensor wasn't plugged in.
Spark plugs changed, except one. Coil boot stuck in the plug. There's some adhesive Infiniti uses to keep them in place.

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Follow up. Got a new knock sensor to swap out the supposedly damaged one. Took off the intake manifold. That screw in the back was ridiculously difficult to remove.

Took off the manifold and what do I see? The knock sensor with no plug attached to it. Plugged it in.

Then I went to work on the plugs. That odd /driver side was a bear. The "front" one, no. 7, was the most difficult because of the wire loom. Pulled a bunch of clips to finally get a decent angle. Also, had to buy a new plug socket. The one I had was too short by 1/4 inch.

Seems the coils have something like a sticky ring that was used to adhere to the plug. The coils took a little force to pull out. Unfortunately, the coil boot on 6 got stuck and I couldn't get it out. The coil came out, but the little rubber end was stuck.

I finished everything else though. I'll have to figure out how to get that boot out and finish the job.

So, in the end, it was the original mechanics fault. He forgot to plug the knock sensor back in after replacing the starter motor. Also found a screw he apparently lost. It went to a wire harness attachment plate.

Thats great news. I hear you on those coil boots, when I replaced my plugs, I had 4 of those damn little end caps stay in the plug hole. I had to use long thin surgical scissor clamps to grap onto them and pull them out. There was only one I couldn't get to come out, so i went to home depot, bought a copper pipe that fits down into the hole, I cut the pipe long ways to be able to open the pipe to the exact size of the plug hole, i slid it down the hole, and spun it to break the glue loose, then I was able to do what I did with the other cap ends, used the surgical scissor clamps and was able to finaly get that piece out. What a stupid idea Infiniti had on putting a dot of glue on each coil boot. Either way, glad you got the job done

thanks! it was annoying that the knock sensor was unplugged. thought that's why i paid a professional, so i wouldn't have to deal with that. then pay an additional $150 for them to tell me something is wrong w/ the KS and it's not their fault.

anyway, i did see someone selling this expensive tool that is supposed to do what you did with the copper pipe to get the boot out. i'll look into your idea. thanks for the support!