P0300, high idle,
 

This nismo is killing me.

Cel came on over 2 weeks ago. I replaced the spark plugs as a first step in finding my multiple misfire issue.

Cel came back on next day, fine. I order coil packs but in the meantime my fiance convinces me to just take it to Nissan. I do.

I drop it off to perform a diagnostic on the ecu. They tell me an hour later it's idling high and they performed a learn on the ecu and cleared the code.( the service tech is convincing me someone either plugged in my ecu and messed with the stock tune or I've had my motor swapped) I tell them no, none of that.. I bought the car at 7 miles.

5 days later, same issues, cel on, p0300 being thrown, high rpm at idle 1100-1300, horrible gas consumption.

I take it back and the service tech takes it over the weekend to only call me today and let me know that i need to replace the left and right throttle body.

I figure it wouldn't hurt to just clean the TB, replace the intake filters, and carefully clean the maf sensor.

I've never had any issues other than the steering lock mechanism failing. I am currently at 51k miles.

My question is.. anyone having TB issues? Has anyone replaced the TB?

I've heard of this with 350s. It was always after someone moved the plate in the throttle bodies while cleaning them though. The idle position would never reset no matter what relearning procedure was performed and eventually they had to be replaced.

Is there anything that might have upset the butterfly valve in the throttle bodies? Or did you unplug them for any reason then start the car?

Bad AFR sensor. Ive seen this before personally.

I've had to have one of my TB's replaced....it was putting the car into limp mode but without the cel. All good after replacement.

EDIT: correction, yes it did throw the cel's....i was thinking of a separate occaision where it went into limp mode without cel.

My fiance and I were really careful about the sensors and the throttle bodies when doing the spark plugs.. he did the passenger side and I did the driver. We didn't clean.

The only strange thing is that it was idling high, eating up gas, and cel was on before the spark plug change. Prior to that I had never touched the TBs.

I guess we'll see the verdict when I pick her up today.

I have a good idea youll find it to be the AFR sensors on the headers.

I had the same thing. I was averaging like 16mpgs and idling at 1100rpms and had a reoccurring CEL.

no limp mode here.. at least not yet.

... nah, too easy.

yup.. 15mpg, around 1100, cel wont go away. lol


I guess I'll post up the fix as we find it.

DAT Ferrari gas mileage. haha yeah. I mean its hard to say over the interwebs but I think that's the issue.


If that's the case get the AFRs from FB Nissan here on the forum. Cheapest genuine parts Ive found.

Did you check around for vacuum leaks? When I installed my intake manifold, it didnt torque down corrrectly and I had a leak on the intake manifold seal so I had to readjust it. I dunno if you took off the intake manifold to do the plugs or not but if you didn't use a new seal, thats one spot to check.

I didn't take off the intake manifold.
I want to go over everything myself when I get it back.

OP, any mods? intake/exhaust, etc? This code is generally thrown with an aftermarket intake.

There's multiple places you can get a vacuum leak without removing the manifold.

The symptoms you're getting are strongly indicative of either

A: A sensor failure somewhere in the closed-loop system.
- MAF sensor
- Primary O2 Sensor
- MAP sensor (unlikely)

B: Vacuum Leak

C: Horrific exhaust leak at the header/head interface...very unlikely. You'd hear/smell/see it immediately. And you'd probably catch something on fire eventually hahaha.

no intake and no exhaust. no mods that would directly have a connection. Only suspension

I'm not jumping to throttle bodies' replacement as quickly as nissan. i mean MAYBE an exhaust leak somewhere considering I maxed out my coilovers.. i could have hit the exhaust but I don't hear anything high pitch when I get on it.

we shall see. still haven't gotten a call to pick her up.




MAP? is it the sensor by the right throttle body?

its the sensor on the back driver side of the intake manifold. You have to take the top part of the intake manifold cover to see it. Its plugged in and held in by a single screw.

According to Nissan, if it's not bad spark plugs, they now don't know what it is. They are replacing the spark plugs hoping they were gaped wrong.

oh joy

I had to drop the gap on my plugs. they were getting blown out at 7700 rpms. all good now :-) Did you buy the plugs from Nissan?

Chris, what was the symptom of spark blow out? Also, how damned high are you spinning it???

I would have seafoamed the car as a last ditch effort....in for the results. Good luck!

Running this bad boy to 8k and I make power all the way till then. Basically it was very clear in the dyno chart where it would cut out real bad in the pull. It would dump rich right at 7700 and be normal. Created a dip in the dyno chart multiple times between 7700 and 8k. Even once at 7500. Tuner charged me $50 and told me to bring it back after I dropped the gap in the plugs. Sure enough, runs smooth up till redline after I dropped the gap to .026 and he was able to get a better tune out of it to the top. The 4.08 gears with the 8k redline should be a wonderful pair :)

No I had hks


-v and her z

At that point I would definitely side on the issue of bad/dirty MAF sensor(s) or faulty O2 sensor in one of the cats. You should not be throwing this code in an unmodded car.

If those are fine, like others have said, I would check the coil packs and also for vacuum leaks.

Heard from Nissan this morning- last word is fuel injectors.

Sounds like they're just crossing off things on a list.

Ya, I told him to stop guessing and have my car ready for pick up.

what a headache

Your idling high because your car is LEANING OUT, most definitely start with vacuum leaks, hoses throttle body intake manifold. Move onto sensors that read air flow, I.E Bank 1 Air Fuel sensor and bank 2 Air/Fuel sensor. Next move to MAF's(not likely as you would throw a Air Fuel code and the air fuel sensor.

Bottom line
1)Vacuum leak
2)Sensors monitoring vacuum and air
3)Exhaust leak BEFORE A/F SENSOR
4) Fuel drop off causing car to throw more air through the chamber

Check by disconnecting MAF's and seeing if idle changes or fluctuates at all that will rule out the sensors.

First off, this is a 7 month old thread that was already resolved.

Second, you're re-hashing what others have already said (including myself in a bulleted list on the first page).

Third, in testing I've performed since this thread was concluded, I can actually say that MOST vacuum leaks on this car, the car will adjust idle around it and stabilize somewhat close to the commanded idle speed unless the leak is absolutely massive.

Case in point, i can disconnect one of my catch cans from the intake manifold (big nipple on the front of the plenum), and briefly (3-5 seconds) it will surge up to around 1800rpm, but it will quickly adjust and go back to almost normal.

This wasn't something I was doing for fun, was doing some diagnostics, and I never tried disconnecting both of them, that would likely be too much of a leak.

Anyway, yeah. Thread is over and done with anyway.

It was resolved? So it was fuel injectors? I didn't feel like that ending was very conclusive....some details would have been nice, how many fuel injectors, what was wrong with them etc.

And honestly who cares how old a thread is? The OP may have solved their issue (maybe?) but chances are that someone who comes across this thread is experiencing a similar issue, so all the input is appreciated, even if it doesn't apply to OP.

I installed an oil cooler and the p0300 popped up first start up thank it was a coincidence. I replaced the spark plugs and the code came back after a day. I replaced the coil pack and the code came back after like 2 weeks. Not sure if the oil cooler has anything to do with it but I'm just not sure what direction to go in


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I have an oil cooler as well, but had the P0300 issue before installing it (and after). I don't think that is the problem.