04 DE MT6. Car has about 110K miles pretty much stock only mods Greddy catback, JWT pop charger. I get this hiccup every so often when im at idle. Sometimes it does 2 maybe 3 times back to back then nothing. It may go days or sometimes weeks without doing it but i only notice it when im stopped at a light or parked. No codes are present or pending. Car runs great with not issues. I did lift the car one day and got under to hear/inspect this more and when it does this hiccup/miss fire i seem to hear it coming from the transmission. It sounds like a metal clunk when it hiccups but not loud and you can feel the engine kinda jerk. This may be a miss fire and maybe a sensor going out like cam or crank but again no codes. This has been happening for a while now and I havent really been to concern about it but it does make me wonder what this is. Again the car runs great. It idles solid and the engine seems to function very smooth. I dont run this car hard and I keep up with the maintenance. What do you guys think?

 

What kind of code reader are you using to perform a scan? Might try another type to see what codes pop up. Also, can you describe more of the maintenance performed, such as when were plugs changed and coils checked?

 

Im using an Ultra Scan gauge. Ive used this on all my cars and its pretty legit of course not like those expensive scanners from a shop but works good. I changed spark plugs last year. Ive had to replace one coil because It did throw a code and the car performance was affected by it but once it replaced it with a new one everything was back to normal and the code cleared. Other than that I have not done any other maintenance other than oil changes, transmission and diff fluid change along with suspension work. Im the second owner of the car. When i bought it it came with a maintenance history. Seems like the previous owner kept up with the maintenance throughout his/her ownership.

 

When you changed sparkplugs, did you check on the condition of the valve cover plug gaskets? If they were worn and leaking, it could be another source of a misfire.

 

I also replaced the valve covers with OEM ones under a year ago

 

OK- sounds like you've covered most of the mechanical bases on the engine. But I've never heard of the transmission causing a change in the idle, but it sounds like that's where you may have to examine more closely.

 

From the inside of the car it does seem like a misfire from like bad coil or maybe a spark plug but when I heard it from under the car it seems to come from the transmission and like a faint clunk. Just weird. I believe it still has the oem clutch but im not 100% sure. Again car runs great im just trying to see if this is something i should really be concerned about or carry on.

 

If, as you say, the "faint clunk" is only occasional so it's hard to imagine being too concerned about it. Maybe you can lay down under the car and listen for some kind of pattern, but unless it becomes more frequent or urgent, I'd say you leave it alone.

Earlier this May, I drove my Z on an appointment and only a block away, had a misfire come up. Drove it straight back to the garage and swapped cars. Ended up scanning it with UpRev Cipher to find a P0304 code. While I'd swapped NGKs back at 90K, I ended up checking everything else and replacing the #4 coil. My '03 Z is running well again, but I try not to sweat the small stuff. Now the big stuff gets all my attention and I don't waste time fixing things.

 

dKmura thank you for your input on this. I'll just continue to monitor this and if it worsens or other issues arise I will look more into it.

 

My pleasure. Keep us updated on whether this gets worse and what the outcome is. Z33 mysteries gain an audience...