Okay guys any help would be great:

Went to change the spark plugs on my car (has about 80k) and now the car is misfiring like crazy and throwing code P0300 (multiple misfire). Car was working perfectly fine before replacing the spark plugs

Steps I've done to correct:
Verified all coils are sparking by taking them out and verifying a spark
Checked for RPM drop by disconnecting a coil individually
Replaced the old spark plugs

Tried driving the car about 2 miles. Car started and idled at 1k. After driving about 2 miles noticed significant power drop and also car idled at 500rpm.

I'm running out of ideas... thoughts, suggestions?

 

Any oil in any coil pack? also, did you bend the coil packs when you put them back in? Are they seated properly?

 

Unfortunately yes to both questions....

Small amount of oil. I tested the coil packs though with them removed from the engine and they all spark...

 

they are seated properly... removed and put them back in at least 5 times

 

I know this sounds weird, but It could be the MAF sensor. It happened OVERNIGHT. Drove to San Antonio (145 miles), ran fine, then next moring, runs like ****. Mine started doing the same thing. Start and idle high then down to 500 rpm. Runs fine at WOT. At steady state throttle, there was a random miss and some time when you accelerate in third or forth, it would just die for a sec then recover. Turns out the MAF sensor was bad.

 

There is a problem with the gaskets in the vq's where oil gets into the spark plug, it happened to mine, there is a sticky on the sedan forums about it.

Also, if you bent the coil pack you may have damaged the pack even though it maybe sparking, it may not be sparking well enough to fire a cylinder.

 

This is the thread pertaining to the oil leak problem.

https://g35driver.com/forums/engine-...rranty-up.html

 

I did read the thread about the valve cover and thought about it as well....

only thing I would question is that the car was working perfectly before this. i was just doing it as routine maintenance, so how could this have caused issues now?

 

What spark plugs did you use?

 

This happened to me, It ran fine no plug changes til 120k I changed the plugs and found oil, put new plugs in and they misfired on 2 cyl.

Also did you use recommended spark plugs?

 

this is why I dont want to change my spark plugs. Im running good at 103K and am worried i might have this type of experience once I change the plugs

 

Hmm - MAF sensor may be a possibility. After I drove the car yesterday now I am getting error code P0102. It came up once before but I think it's because I didn't have the intake connected. I suppose I may have damaged the MAF when removing the intake? Texasscout how did you figure out it was the MAF sensor? Also did you car run roughly even at idle? The code doesn't stay consistently so I'm not sure of that is the issue and rather came up when i had the intake disconnected. Also my car is always running rough even at start so I'm not sure if your problem is a 100% like mine however it is similar

I'm using NGK Iridium Plugs, I checked the gap on them and is good. Also I tried putting the old plugs back in and same problem.
I've talked to some other people and they mentioned a potential problem with the cat... also seems unlikely to me.

I think top 3 problems would be:

1. Gasket - I just don't understand why this would be a problem now when it wasn't a problem before. I've talked to some other G owners who have had oil in their cylinders. To my knowledge unless it's an excessive amount the cylinder should still fire.
2. Damaged coil - somehow damaged the coil, just when I tested them all of them are sparking strongly. Also checked with a multimeter and all of them are showing correct resistance.
3. MAF sensor - it's a possibility but the error code isn't showing consistently.


All of them seem to have an issue which makes me think that's not the underlying problem... just trying to nail down a concrete answer... any other thoughts?

 

also btw I apologize, but I actually have an '04 Coupe, I accidentally posted in the sedan section... but should be the same anyways.

 

Did you change the plugs one at a time or remove 2 or more at one time? If you did, maybe you mixed up the firing order on 2 plugs so it runs, but is missing on 2 cylinders. I would verify the firing order and make sure you reinstalled the coil packs in the correct order.

 

I did change them one at a time so I don't believe it's the firing order. Also, I'm not sure how anyone could really mix up the firing order since the cables to each individual cylinder are so short. I noticed the passenger side are labeled 1 3 5 but my driver side for some reason is not. Just to double check is there any way to verify I have the correct firing order?

I'm still 99% positive it's correct especially because the cables won't even really reach to the other cylinder.