Rough idle/stumble at low RPM on my 2003 M45

[Tim/M45]

I've been reading and researching my problem here and seem to have overloaded my brain. Lots of great info here but I need to narrow it down, with some good advice, before spending more $$$.

Recently bought the car, has 98K miles. Has several unrelated problems (I think) which I will get to in time, but for now I need to fix the rough idle. It only happens after the engine is warmed up. I do not notice it at cruising speed or after I start to accelerate, but at a light it seems to stumble and missfire until I get moving again.

I only have had one code for a missfire which I cleared a couple weeks ago. Has not recurred.
I have checked and cleaned the plugs. They are Denso platinum and look almost new, .043 gap.
When pulling the plugs I found one coil pack was sitting loose in the hole. (same cylinder that threw the missfire code). Someone stripped the threads. I re-tapped the threads so it is in tightly now. This did not fix the problem.
I cleaned the MAF sensor and throttle body (big mistake, think I screwed up the TB). Now I have the fast idle problem too. I have checked pretty well for air leaks, but could have missed something. It has a slight oil leak from the right valve cover gasket. Could it be sucking air?

Ran a can of BG through it, but no joy.

It was a one-owner-car, which the dealer says was well maintained. They did the instrument cluster recall and the "connector" recall ( I believe this is the cam sensor recall).

I am contemplating trying new plugs, then new cam sensors. I can also get another coil pack and R&R it with each of my old ones to see if it isolates the problem. Any comments and suggestions will be greatly appreciated.

Thank you.

[EdBwoy]

Quick comment, which might or might not solve your issue - those spark plugs. In all my research & ownership of Nissan vehicles, they do not seem to bode well with anything other than NGK spark plugs. NGK plfr5a plugs might be a good start.

[Tim/M45]

Thanks EdBwoy. I was leaning that way after seeing a lot of comments about NGK being preferred.

[BlackCat81]

Your high idle after you cleaned the throttle will need a idle air volume relearn done, if it will even work. The throttle bodies on all Infiniti cars are EXTREMEMLY sensitive and I can't tell you how many I've replaced over the years from third party repairs shops bringing them in after cleaning the throttle body and not being able to get it to run right. Whatever cylinder is misfiring, try swapping that coil with another and see if it follows. That'll at least rule out the coil. I agree with a previous comment, these cars are also very particular with spark plugs, so I'd go back to NGK's.

[Double E]

NGk & Do the throttle re-learn procedure. It CAN be done yourself but the process is frustrating and though I was once successful in doing it myself, I would pay the dealer to do it again. Call to ask for the cost of the procedure first. You will not hurt it by trying it. it will NEVER run right till that is done. Do check for any air leaks too.

Just to be sure...the coil pack mounting hole is stripped, not the spark plug hole? Ziptie that sombitch in place if so.
The leaking valve cover gasket is more likely going to push air if anything so It is not the cause.

[Tim/M45]

Thanks all.
I picked up the NGK plugs tonight. I'll change them out tomorrow and try the throttle relearn again (I've tried it several times already). If no joy I may have to get the dealer to do it so I can get past the idle issue.
I'll post my results.

[BlackCat81]

The car has to be warm, in closed loop operation. Turn all your accessories off, including the radio, heat or a/c, headlights, and make sure your heated or cooled seats are off. It also won't do the relearn if the check engine light is on. It really helps to have battery voltage over 12.5v as well.

[Tim/M45]

I replaced the spark plugs yesterday. No change. Still missfires at idle. It does not throw a code for missfire though. I'm still trying to get the throttle relearn done correctly. While I was changing the plugs I noticed one of the coil packs was different. 7 were the Hanshin brand. One was not. I forget the brand, I think it starts with a "D". Anyway, that coil pack was on the cycinder that did throw the missfire code a few weeks ago. So,I think my next step is to replace it. Are there any preferred brands? OEM from Infiniti looks to be about $95, whereas I see them online for about $50 (Hitachi).
Thanks again.

[steve_c]

Tim,
How did you make out with the new coil? Did you go with the Hitachi? Did the missfire go away afterwards?

[Tim/M45]

I did not change the coil yet. It has been running fine today. Missfired and sputtered a bit first timeout yesterday after changing the plugs, but no problems today. Also, I was finally able to do the throttle relearn successfully this afternoon. The car is running well, for now. I will drive it this week. If it missfires again I will order the coil. Still not sure which brand coil to get.
The TB was wet with oil residue when I did the plugs, so I am leaning towards installing the oil catch can. I imagine the intake is pretty nasty downstream from there. nAny suggestions on cleaning that?

Thanks to all who gave their input. I love this car. I have been looking for one in decent shape that I could afford for the past 2 years and am very happy to finally have one.

[BlackCat81]

I did not change the coil yet. It has been running fine today. Missfired and sputtered a bit first timeout yesterday after changing the plugs, but no problems today. Also, I was finally able to do the throttle relearn successfully this afternoon. The car is running well, for now. I will drive it this week. If it missfires again I will order the coil. Still not sure which brand coil to get.
The TB was wet with oil residue when I did the plugs, so I am leaning towards installing the oil catch can. I imagine the intake is pretty nasty downstream from there. nAny suggestions on cleaning that?

Thanks to all who gave their input. I love this car. I have been looking for one in decent shape that I could afford for the past 2 years and am very happy to finally have one.

I wouldn't necessarily order a coil yet, I'm surprised you have a noticeable misfire with no code. If it returns, swap the coil with another and see if it follows it, unless you're just wanting to replace it. Sometimes when you have a miss on first cold start it can be a sign of coolant pooling in a cylinder from a possible head gasket. One of the other techs is currently replacing a head on an FX50 for symptoms similar to yours. Not to freak you out, as that would be EXTREMELY uncommon.

[EdBwoy]

I did not change the coil yet. It has been running fine today. Missfired and sputtered a bit first timeout yesterday after changing the plugs, but no problems today. Also, I was finally able to do the throttle relearn successfully this afternoon. The car is running well, for now. I will drive it this week. If it missfires again I will order the coil. Still not sure which brand coil to get.
The TB was wet with oil residue when I did the plugs, so I am leaning towards installing the oil catch can. I imagine the intake is pretty nasty downstream from there. nAny suggestions on cleaning that?

Thanks to all who gave their input. I love this car. I have been looking for one in decent shape that I could afford for the past 2 years and am very happy to finally have one.

My coils are Hanshin, and maybe someone might be able to offer counter-Intel on this, but I've not noticed many, if any issues with the coilpacks on our cars. Knowing that someone replaced that one coilpack, seems to call to another issue that someone tried to remedy with a coilpack(ever find out who the manaufacturer of that coil was, Duralast perhaps?). How's the injector firing at startup?
Might you have also replaced the PCV? One symptom of faulty PCVs is oil on the intake air side, like throttle bodies.
Oh, and also I believe the car needs at least 2 key-ignition cycles to throw a code. If all is clear, I would run some seafoam to clean up. I've had success with the product personally.

[BlackCat81]

I did not change the coil yet. It has been running fine today. Missfired and sputtered a bit first timeout yesterday after changing the plugs, but no problems today. Also, I was finally able to do the throttle relearn successfully this afternoon. The car is running well, for now. I will drive it this week. If it missfires again I will order the coil. Still not sure which brand coil to get.
The TB was wet with oil residue when I did the plugs, so I am leaning towards installing the oil catch can. I imagine the intake is pretty nasty downstream from there. nAny suggestions on cleaning that?

Thanks to all who gave their input. I love this car. I have been looking for one in decent shape that I could afford for the past 2 years and am very happy to finally have one.

My coils are Hanshin, and maybe someone might be able to offer counter-Intel on this, but I've not noticed many, if any issues with the coilpacks on our cars. Knowing that someone replaced that one coilpack, seems to call to another issue that someone tried to remedy with a coilpack(ever find out who the manaufacturer of that coil was, Duralast perhaps?). How's the injector firing at startup?
Might you have also replaced the PCV? One symptom of faulty PCVs is oil on the intake air side, like throttle bodies.
Oh, and also I believe the car needs at least 2 key-ignition cycles to throw a code. If all is clear, I would run some seafoam to clean up. I've had success with the product personally.

Ya, coil issues are few and far between. PCV issues are also uncommon, but they can cause oil in the intake and throttle body. A light coating on both is normal though, I've never had an intake off that didn't have oil in it. A check engine light can be tripped instantaneously, especially for a misfire. Other codes can take various amounts of time to trip it, so you're not totally off base.

[steve_c]

In my case, 2006 m35x, I was getting a cold start up miss on occasion. Especially when car was parked a few days unused. It would straighten out on its own after a few minutes, no CEL. I started car last week, idle was rough, did not clear up, followed by flashing CEL & code PO304 cyl. 4 misfire. That is what I have now. I've got 115,000 miles on odometer, plugs never changed. I figure I will start with coil changeout (bought 6 Hitachi's) since I will be installing new plugs. Waiting for parts from RockAuto, but I am concerned it could be another issue. I removed #2 & 4 coils already, going to pull plugs tomorrow to see if any indication of coolant leakage into cylinder 4. I did not swap coils to see if problem moves with the coils. I am second guessing myself now, I should have swapped before ordering a new set.

[Tim/M45]

I only noticed the missfire after the engine was warmed up. It was so bad I returned home and left it there until I could change the plugs. I only got the one missfire code. I did put the suspect coil pack on a different cylinder when I changed the plugs. My coolant level is steady, it is my oil consumption that concerns me next. I will fix the leaking valve cover gasket and install the catch can (and replace PVC valves) next.
As for the Seafoam, do I hook up to the PVC input to the TB?

[BlackCat81]

I only noticed the missfire after the engine was warmed up. It was so bad I returned home and left it there until I could change the plugs. I only got the one missfire code. I did put the suspect coil pack on a different cylinder when I changed the plugs. My coolant level is steady, it is my oil consumption that concerns me next. I will fix the leaking valve cover gasket and install the catch can (and replace PVC valves) next.
As for the Seafoam, do I hook up to the PVC input to the TB?

You can do it that way, or you can run it through the PVC hose. If you've never done it before, there's a super fine line of using too much and causing it to stall, so just go easy with it. I haven't done my Infiniti, but I did my old 4Runner with it. It didn't smoke much during the process, but if you let it sit a while after you do it it'll smoke like crazy when you first start it, so be prepared for that.

[EdBwoy]

I only noticed the missfire after the engine was warmed up. It was so bad I returned home and left it there until I could change the plugs. I only got the one missfire code. I did put the suspect coil pack on a different cylinder when I changed the plugs. My coolant level is steady, it is my oil consumption that concerns me next. I will fix the leaking valve cover gasket and install the catch can (and replace PVC valves) next.
As for the Seafoam, do I hook up to the PVC input to the TB?

I usually use the vacuum input from the brake booster to the intake manifold, after the check valve... but I wouldn't do the seafoam in this case yet.
I haven't used it for major misfires, only for cleaning carbon deposits.I would try to fix the misfire first. What did you find out about your injectors?

[Tim/M45]

I have not checked the injectors yet. That had not occurred to me, but it seems as likely as anything else. Is there a test I can do on my own without special tools?
The noticeable improvement I had after changing the plugs, and making sure the coils were in tight, makes me think the issue is related to ignition.
I appreciate the input. Thanks.

[EdBwoy]

Well, there's the good olé screwdiver test. I actually use a long metal rod that was part of a pathfinder jack. Just place one end of your solid object against that suspect injector and maybe 2 others that you can easily access... and the other end safely against your ear. Not too scientific, but the aim is to hear the injectors clicking at approximately the same frequency.
This is just me following the line of one replaced coil. Another thing that occurred to me, how are your vacuum hoses? Do you hear any hissing from the engine? There are also other simple ways to identify vacuum leaks in case those are dry, brittle and cracked; such as using starting fluid.

[Tim/M45]

I'll check the injectors and look for vacuum leaks next.
I learn something new every day. Thanks.

[Tim/M45]

I pulled and cleaned the PCV valves. Both were clear inside, the ball rattled, and closed appropriately when I applied a little suction. I assume this means they are OK. I reinstalled them. I found one cracked hose in that line and replaced it. No change. Still getting missfires occasionally. Not as bad as before. Can someone enlighten me about the 2 larger hoses coming from the top of the valve covers towards the rear of the engine? They join at back of the drivers side valve cover and go into the intake UPSTREAM of the TB. What is this? Seems redundant.
As always, thank you for you input.

[Tim/M45]

One last update:
I finally got the rough idle to stop. I had replaced one suspect coil but it kept up with the intermittent rough idle after the engine warmed up. I took it to Infiniti and they told me it needed a full set of coils, $1,700 installed. I said no thanks. Ordered a set of OEM, used on e-bay for $180. Installed them last week and it cured the rough idle. Yeah!

I still have the high idle after cleaning the throttle body though. I will start a new post to seek help there.
Thanks.

[onelly23]

I m having the same problem on my fx35. I dont have codes but it have a hard start at first try but starts engine at second try, it also misfires at a stop light, when reversing and sometimes in park, but it improves a bit when in neutral. I replaced coils as they go bad, but haven't replaced all six at once like you did. I wanna know if the problem came back after replacing all the six coils, so i can risk replacing mine too.

[Tim/M45]

The problem was solved by replacing the coils. Ran fine after that. I actually only had one that was bad. I was able to get a full set of 8 used on e-bay so I have the extras collecting dust in my garage. There were after market coils available new but they were slightly different than OEM (shorter) so I went with OEM coils,