Hey guys, I'm very new to the z world and love my z. But I'm plagued with an idling issue. I have an 04 350z with 151,xxx miles and the only mods I have are a high flow intake and an exhaust that were already on the car when I bought it. So here goes the list of things I've done in order to fix the issue:

I started with the pcv valve since it was cheap and available. It didn't really improve the issue, but figured it needed a new one.

Then I noticed a CEL pop on. Got it code scanned, it came up with a MAF code. So naturally, I figured a new MAF would help. But I noticed my rpm's go lower from 500-450 to about 400-300. So I did the pedal dance to see if it would improve. Of course, it didnt. So I moved on.

Next, I cleaned the throttle body and did the idle reset and noticed a significant improvement. It started to idle at about 750-600 and stayed pretty steady. It would still drop and almost stall when I pulled it out of gear but when it picked itself back up, the idle was normal. I stopped to grab dinner, then the car wouldn't idle at all when starting it. It would kind of stumble and jump between 0-500 but never stay steady and I could smell gas. I did a little reading and research, and discovered when the TPS starts going out and gets hot, it displays those symptoms. So I let it cool off, and drove it home.

Because of the irritating stumbling issue it displayed, I figured it needed a new throttle body, so I replaced the throttle body, cleaned up the extremely dirty intake and plenum, installed new gaskets, and did the idle relearn. I noticed better throttle response, but the idle sat around 400-300 kind of steadily, but still stalled when I put the car in neutral. I've done the idle relearn 2 more times to make sure it wasnt the issue and every time the idle still drops to 400-300 after it warms up. The car also likes to just die while it's in neutral and moving. While trying to start it, it stumbles and doesnt have any power and dies as soon as you let off of the gas pedal.

I should also mention that I bought the car with o2 sensor code and fixed those almost immediately and didnt have a problem there after new o2 sensors were installed on the right side bank. I had it code tested after I put the new throttle body in and cleaned everything because a CEL had popped up again. It came up with P0183, P0462, P0507, U1001. I cleared the codes and the light has stayed off, but I dont think I've driven it enough after that for the light to come back.

I've also checked for vacuum leaks, and couldn't find any. I also made sure all of my connections were tight and everything was clean. So that's it. I've pretty much gone through the whole intake system and still have the issue. I'm stumped and don't know what else to do. Ive spent countless hours searching google trying to find something and most people dont have the same issue I'm having.

I know I have a lot of stuff in my post, but I figured I'd be as thorough as possible so that the issue was explained as best as possible and whoever's read this knows what I've done in hopes of fixing it. Any thoughts? Anyone else have these issues before that can shed some light? Any help would be appreciated and will be listened to.

 

I had the same issue on my '03, and I would advise making sure all the bolts on the plenum are torqued to spec. There's also a bolt pattern, but I figure your issue is a vacuum leak.

https://www.z1motorsports.com/upload...ll%20guide.pdf

It might be worth checking the exhaust as well for any leaks there.

 

OP, buy a vacuum gauge at O'Reilly's or Harbor Freight for $10. Plug it into your intake vacuum lines. It should read steady at 23 or more.
If the needle swings a lot with rpm you have an intake air leak.

 

Thanks for the replies guys. I kind of leaning towards something with the vacuum because I did get a live reading and it showed it was running lean. I'll get a vacuum gauge and see what it says and report back. I'll also get a torque wrench on the bolts too just to double check everything is all tight. Never hurts to double check something like that

 

Ok. So I figured I would see how the car acted for a few days before I posted again. But I tested the vacuum at start and at idle. For both, it held at about 17.5 to 18 ng. I know that the higher the altitude, the lower the pressure. I'm not too sure if that's normal for colorado, but it held consistently with no drops while idling. All day yesterday and today, the car acted normally and held a decent idle. It even got to the point where I wouldn't have to ease the rpm's down to shift into neutral. I was able to just put the car in neutral and it would hold at 650. But I guess my negative terminal lead wasnt secured tight enough and the negative battery cable came out of the lead while driving to the gas station. After that, the idle began to stumble here and there, so I didnt the pedal dance to relearn the idle. When I pulled the car in front my house, it started to stumble pretty bad. Does it take a while for the car to relearn and keep consistent even after doing an idle relearn?

 

Post a picture of your intake. If someone put a 4 inch intake on their and never bothered with a tune it might be the main culprit. For some reason 4 inch intake pipes are all the rage lately in these cars.

 

It doesnt look like it's a 4 inch. The car ran fine for a while after fixing the lean issue it had on it. Now its throwing p0172. I'm swapping the new MAF back into the car. It was switched back before the intake was cleaned and I'm going to clear the code and see how it runs

 

He hasnt been on the site in 2 months but im using this EXACT intake and im having the same issue..

 

Ended up figuring out what was causing issues, my ecu was messing up. Kind of figured it out by accident. I had unplugged the ecu overnight and everything seemed fine after I plugged it back in. Idle still drops after romping on it hard and just straight up shifting into neutral from doing that, but otherwise, everything is all good now. It could probably use a tune though

 

So you just unplugged your ECU for a bit and that solved the problem? Im not sure exactly what your issue was but it sounds very very simaler to mine. Only dos it when the car is fully warm. So lets say i rev it to 4k will sitting still, it will fall the way to 200-400 and struggle for like a second then pop back up to normal idle. Same thing if im driving normal in lets just say 4th gear and i pop it in neutral and come to a stop sign. Ive cleaned maf , throttle body ETC, Checked hoses and all.

 

That sounds exactly like the issue I was having. Except, my z would just completely stall out and I'd have to start it back up again. I replaced a lot of sensors and components before I unplugged the ecu. I replaced the throttle body, vvt solenoids, maf, camshaft position sensors, pcv valve, the hose for the pcv valve, cleaned the intake and plenum and replaced those gaskets, valve cover gaskets, catalytic converters, 02 sensors, and spark plugs. I thought it was a vacuum leak for a long time. My fuel trims were way rich too. They were at +20 long term and short term on both banks. I almost started replacing everything with the fuel system to even out the fuel trims. What I would do, is put a decent scanner on it that can read fuel trims. I bough the bafx bluetooth scanner on Amazon for like $20 and bought the torque pro app for $5. The torque pro app was able to show me my fuel trims in mostly real time. Sounds to me, you're running rich. All that happens with the ecu when you unplug it, is it totally resets. If you choose to try it and see if it works, unplug the battery by removing both leads and you can either pull the ecu, or hold the terminals together for 30-60 seconds after you undo them from the battery. I cant stress this enough, it was an accident on how this was fixed for me. It may or may not work. Plenty of people say your car doesnt need a tune after putting in high flow intakes and performance exhaust, but these nissans are touchy and even swapping 1 sensor can throw your ecu off. So my honest opinion would be to get the car tuned at some point, just to be safe. I know it sounds like a PITA and expensive for just an intake, but itll be worth it in the long run. Especially if you plan on installing more mods.

But please let me know if you try it and it works. I'm curious to know if it's something that's kind of a "solution" to an issue like this. I've never seen anything on it with all the research I've done on the matter

 

I do have code P0183 (Fuel tempature sensor) Not sure what that is or where it is lol or if its linked to my problem

 

The fuel temp sensor is a part of the fuel pump in the gas tank. It shouldn't cause an idling or engine performance issue. I had that code pop up once with like 3 other codes and it never came back after I cleared it

 

that style of intake filter doesn't allow for laminar flow to that maf, it will be wildly turbulent air.. ( there's no venture behind the filter like on a JWT) AND... it loves to throw filter oil at the maf.
I opened this thread ready to comment " what crummy ( no offense meant at all) intake do you have, or you have a vacuum leak."
You sound like you've researched the common issues, but vacuum leaks can be a b*tch on this weird plenum , and hoses do tend to leak especially at hi mileage like that. Also, leaks can come and go due to heat expansion on the plenum etc.

In all honesty, if you have a mostly stock car otherwise, find a factory airbox and reinstall, it is hands down a better intake for this car than anything else out there until you get VERY modded.. and it comes with ZERO problems or gremlins.
The sheer numbers of young kids who buy intakes as their first mod means factory airboxes are often FREE if you post a WTB on the FB groups.

 

While I do agree with you, I bought the car with that intake on it. I would love to get something better, but that'll come later after some significant mods. While it isnt the best, it's also not the absolute worst either. If you're getting oil thrown through the intake, then you might have a vacuum leak, pcv issue, and/or a dirty intake. I've also found vacuum leaks to occur on the back side of the plenum more often too

 

I know its been a while, but I wanted to post an update on this. Ever since unplugging the ecu, I haven't had too many issues. Just had it stall here and there, not that frequently, but no weird half dying stuff when trying to take off. The issue was still kind of bothering me, so I started thinking about the issue. These cars are super touchy to intake changes. The only change to my intake, was the high flow intake. Well what changes A/F ratios? Mostly air intake does while the mass air flow sensor makes changes while air is passing. So I looked up what affects the mass air flow sensor to change A/F, and ambient air temp is one of the variables. Well the way I had my intake set up, I didn't have a heat shield. The filter and the MAF sensor were right next to the motor, dragging in hot air while the car was coming to a stop, rapidly changing how the MAF reacted, and stalling the motor. So I decided to buy the JWT pop charger, which comes with a heat shield and a larger filter. I also extended the filter closer to the front of the engine bay. Amongst some of the research I've been doing, I also opted to buy a plenum spacer. Turns out, the stock plenum for the vq35de is slanted forward. So 2 of the cylinders don't get as much air as the rest of them, which can cause a similar issue as I was experiencing. So spacing the plenum helps even out that air volume, and adds a little bit of power (woohoo!!). After installing both the spacer and the pop charger, I've noticed a huge difference. My idle is way smoother, I have more pick up and go, throttle response is way better, I'm getting a slightly longer and better stroke out of my gears, and after really romping on it the car brings itself back down to idle pretty smoothly without dropping below where its supposed to be. Overall, I'm much happier with the spacer and the pop charger. I get great intake noise, the car sounds better than it did before, and its definitely just a tad bit quicker. If anyone else has a similar problem to what I was having, pay attention to your intake. It could save you a very long and expensive headache. I still recommend a tune with this. The car will still benefit from it after all the bolt on mods. A tune will definitely be next for me since uprev will do etunes for NA cars