Hi,

I'm sure this topic has been covered before, but I am reading different things on different posts and thought it might be good to make a new thread. First off, I drive a 2002 Infiniti i35, though to my knowledge it is the same VQ35DE as in the Maxima for the same year. Apologies if this post is in the improper place and I will take suggestion to post elsewhere, however I might get a broader range of experience here than in an Infiniti specific forum, so I'd like to ask anyway.

I have an i35 with 160k on the clock, bought it at 118k. Slowly been running rougher and rougher, especially at idle, and recently decided to change the spark plugs and the boots with them. The plugs were pretty worn (didn't really take time to "read" them, though I kept them, in order, for this purpose), but the coils themselves didn't seem to have any excessive buildup or corrosion on them. I gave the parts store the spark plug number from the technical manual, they said these plugs matched, NGK "laser" platinum plugs, good for 100k. The boots were not the priciest, but they had a lifetime warranty so seemed good enough (at least according to guy behind the counter).

Anyways, long story short, it's up and running, doing greater under acceleration, incredible difference in pickup from stand still and from speed. However, it's still idling rather rough, though probably at the correct idle speed of 650-700. Today I heard the first misfire I've heard in this car at idle. Reading up a bit on what others have suggested, I think I'll consider cleaning the throttle body (though I've read the throttle actuator can be damaged if you tamper with it, I already did so incidentally when i was removing it to change the plugs). I may have a mechanic do this, I'm trying to avoid the stealership.

Anyways, anything else besides that I could try, besides just randomly throwing parts at it, like cleaning the MAF or replacing it? I guess I should mention there is a check engine light, but it for something seemingly unrelated: evap system check valve failure, and the "gross air leak" error code it throws with it. Or could this actually be a reasonable cause? Either way I will be fixing this as well. Any suggestions would be appreciated.

EDIT:

I also should mention I did reset the ECU by leaving the battery unplugged all night, then again once it was up to operating temp by disconnecting the cables from the battery and touching them together for 90 seconds. Hard a hard time starting at first and was really running rough even after idling for 10minutes and then driving steady highway for 15 minutes, though within an hour of drive time it seems to have "learned" and is doing much better. Still I heard the misfire later and would like to track the cause of that down.

Thanks again.

 

I would change back to OEM spark plugs vs an equivalent brand. Was it idling rough before you changed them. Hold this thought on changing out.

You replaced all 6 plugs, removing the plenum, guts, wiring and all? I don't know what your version engine bay looks like, but if so did you reconnected all the vacuum lines? Damaged any? Retrace steps to make sure all coils and vacuum lines are connected

 

Thank you for the suggestion. I actually read out the spark plug model number the service manual called for the shop guy said that was the same. It was idling horribly before the spark plug change. There was actually oil in one of the spark plug tubes and I had to replace the valve cover for that reason. It's running much better, just want to trace it down and resolve it fully now. I'm sure I did reconnect everything, though two small vacuum lines appeared to be damaged, running to a vacuum canister attached to the intake plenum, which itself runs lines to to the "front" of the engine, where it has some kind of vacuum actuator, not sure what this is for though.

EDIT:

Also, the check engine light was on before I changed the spark plugs.

 

This is the right place to post. Under the hood the cars are the same.

The Laser Irridiums are great plugs.

What you're describing sounds exactly like a vacuum leak. Rough idle but great under acceleration.

Any air leaking in to the intake after the MAF housing will cause your symptoms. Check the entire area from the intake boot to all the lines.

You can check for a vacuum leak by spraying brake parts cleaner anywhere a leak could be. When you hit the leak the RPM will surge for a second.

It also wouldn't hurt to clean the MAF. It could be that the plugs were masking the symptoms of the dirty MAF. Usually a dirty MAF will have different symptoms but it's an easy thing to try and should probably be done anyway.

 

Thank you for the suggestion. I thought brake parts cleaner will damage rubber hoses though? Any other way to check for vacuum leaks? I seem to be hearing a small leak near the "front" of the engine, I tried lighting an incense stick and watching the smoke but no luck haha. I will have to take the cover off and look more thoroughly, and also replace the two small vacuum lines and the check valve, which is actually near the gas tank.

 

A little brake parts cleaner will not hurt anything. It will all evaporate way before any damage is caused.

I guess you could use a smoke machine and look for the leak, but that is more work/money. Just use the brake cleaner.

 

Good tips above.

Store brand coils don't play nice with these cars. You want to get OEM Hitachi's off RockAuto (think they're like $30 and change).

The throttle bodies on these cars are fickle b@stards that don't like to be cleaned. Many horror stories on here of jacked up idling afterwards that could only be fixed by the dealer hooking up their scantool/installing a new TB.

 

Mentioned here already... OEM factory Grey Dot Hitachi coil packs are the way to go.

I believe the OEM plugs are NGK Platinums. So not sure Iridiums would cause a misfire though.

If its misfiring, you can pull the codes and it will tell you which cylinder is misfiring. P0301 is cylinder 1. Once you know the location of the misfire, swap a good coil pack with that and see if the misfire changes.

Are you experiencing an irregular idle? Its recommended always doing the pedal reset and idle relearn procedures after disconnecting the battery.

 

Call great suggestions.

Waiting to hear what he finds out.

 

Would the negative battery post removed make cleaning the tb safe? Because I decided to do that on the '03 and cleaned it like I did the '00. No issues with the idle, or anything. Maybe this is a way for him to be able to clean it??? Or maybe removing it and cleaning?

They get quite dirty https://imgur.com/a/DNicv

 

No. Manually opening and closing it can cause damage. It's got nothing to do with the battery cable. Sometimes it's a matter of luck though. I cleaned mine when I first got the car and didn't know better. I didn't have any problems either.

A good TB cleaner spray would be OK as long as you don't poke at the butterfly valve.

 

I only heard one misfire the other day, it might not throw a code from just one. I also had the codes read before this. It is an irregular idle, just a tad bit of surging. I will figure out what is wrong with the vent control valve and fix that first and then get back to this thread with the results. I tried doing the reset/relearn procedure with the gas pedal, pressing it down 3x hard, then waiting ten seconds, then releasing, waiting 7 seconds, then reapplying for ten seconds, but nothing happened. Could definitely tell the ECU had been reset when I connected the battery terminal connectors for 90 secs though. Is the reset procedure different for the Infiniti?

 

Also, there was quite a bit of gunk inside the upper collector of the intake manifold, look really nasty actually, but didn't feel like messing around with it at the time. Is this an issue?

 

uhhhh having the same problem now with the misfire at idle and coming to a stop, so annoying! Changed fuel injectors swapped coils and changed all 6 spark plugs, and changed b2 camshaft sensor. Acceleration is good but misses at idle while stopped in drive but not in neutral.