01 QX4 Has me stumped.

[DrCruelty]

Hello everyone!

Long time lurker here and reading through posts here has helped me solve several issues, so thank you!

But now the bad part. I have an issue that's a bit hard to describe and so far my usually trusty Q is NOT helping me much with clues.

01 QX4, 3.5 with the later style coils, 2WD, 141k. No codes, not even pending ones. Starts without issue. Increasingly, while idling park or even if you're on the highway it will stutter. Sometimes feels like a hardly noticed miss of a cylinder once, to other times it feels more like someone momentarily unplugged 3 or 4 coils and rock you pretty well. There are times it won't have the problem at all. Other times a few times at a red light waiting, and when you're just driving along especially when you give it just a little bit more gas like if traffic thins out and I want to do 50 instead of 45. While rare, it will also sometimes simply fall on its face for a moment under hard acceleration. RPM will rise and you'll be off and then suddenly it drops, and then comes back and rises again.

Trying to use various info from this forum I spent a lot of time tonight trying things as it was fairly actively misbehaving. Due to the frequent MAF issues I even unplugged it and started it back up just to see if it still occurred. And it did, although it did seem to recover from it more smoothly than with MAF attached. Fuel trims are well within reason, no codes of any kind, it seems from the forums these are good for detecting misfires and such and its not reporting any, what IS this thing doing? It's never stalled or anything of that sort, and I've assumed it unrelated to the IACV since it occurs at 75mph as well as idle.

Beyond that, it DOES have significant oil leaks from the valve covers. I've not seen it happen, but could oil be getting into and disrupting anything electronic to cause this but not set any code??

Thanks for any help you can!
John

[hotdawwgman]

I had this issue when coming to a stop and when idling. I would have a rough idle, but it never threw a code. I also had leaking valve covers. So when I did my valve covers, I also replaced the MAF sensor and the PCV Valve. This cured my rough idle issues and of course, the oil leak I was experiencing. When replacing my MAF, I went with the newer version MAF sensor that I believe was available for the 03+ R50's. Used only OEM parts and so far so good. It has been 4 months since I completed this repair. My QX4 is a 2002, btw.

[DrCruelty]

I believe I may have found the culprit. After noticing anything I did to increase fuel flow reduced or eliminated it I took out one of the plugs. I knew the previous owner had changed them not long before I bought it, but I was not prepared for what I found. They are NGK Iridium IX, and recent, but when I looked up the part number it said DOES NOT FIT. The plugs in it fit the 3.3L engine!! Their reach is 0.3" inch too short. AKA the electrode probably doesn't even reach the end of the hole never mind into the chamber. Will update after I change them, but I'd think its almost assured to be the issue.

[DrCruelty]

Plugs swapped with the correct reach and I also discovered coil #6 was a generic replacement with a boot that doesn't seem to fit the cover properly. It has some corrosion on the spring and the tip of that plug was also corroded. Probably was misfiring badly despite the lack of codes. I cleaned the spring for now and ordered an OEM Hitachi coil to replace it. The stumble is gone. Nice and smooth again.