Filled up on 93, no change

 

Got the MAF cleaned and throttle body/fuel injectors cleaned. Still the same. Oh well. I'm not sure WTF else to try but I'm spending a lot of money.

 

this happened to my friend's mitsubishi. He used lower octane than recommended and started to cause problem you have stated. He started using 91 then on and the problem went away. just keep using 91 for a while. the problem won't fix overnight. i remember he started seeing results after 2 weeks or so. some gas stations put additive in their fuel like Shell. Try that. If the problem persists, you might want to look into compression issues or even spark plugs. but please don't panic. this is where the emotional spending kicks in and make mechanics happy. good luck!

 

Thanks akoustic,
Hmmm.. Ok, I would have thought a 100 mile highway trip on the 93 octane would have cleared out any old bad gas out of the line. I got the throttle body and fuel injectors cleaned, too. I'll give it more time.

 

Okay, first things first, 87 octane is not dirtier than premium. If you believe that, you're buying into the advertizing hype. Octane is simply a fuel's resistance to burn. The higher the octane, the more resistant it is to burn.

I recommend running premium in these cars because you'll probably get better mpgs. Why? Because these motors have fairly high compression ratios and tend to run a bit hot. With 87 octane, the motor may detonate/preignite more and when that happens, the knock sensor backs down the timing and adds fuel to cool combustion chamber. This results in lower mpgs. In cold weather, this isn't as much of an issue.

87 octane will not clog in injectors.

With todays high grade fuel, low pressure fuel systems, and underground storage tank regs, fuels are clean as is the combustion process. There is no need to perform fuel cleaning services on these motors and if you read the owners manual, it specifically states not to use these "treatments". I have yet to hear of an injector getting clogged on the VQ35. Additionally, these have the ability to know if there is some sort of fuel issue. If it senses a lean/rich condition, the CEL will be tripped and the ECU will tell you where to start looking.

The VQ35 is not a terribly smooth engine. My VQ30 was extremely smooth, but when Nissan punched out the VQ, it added some noise, vibration, harshness (NVH). What you are feeling is most likely normal. Cleaning the MAF sensor with electronics cleaner and cleaning the throttle body are always good ideas, but if are not car savy, then have someone else do it.

 

Thanks Dave B.
I'm puzzled for sure. Done everything I can think of.

 

hey, anyone have similar issue and fix? my car just started idling louder than before.
engine still runs great, and i have been using 91 octane and not changed for years.

i just had an oil change and they told me my flex pipe was damaged when i bottomed out causing a tiny hole. could this increase the idle vibration and noise? i'm pretty sure i hear it from the engine but they could be right?

 

Morningla,
This sounds very much like what my car is doing. However, I did have my local exhaust/tire shop check the exhaust and they said all looks fine. Would that tiny hole be easily visible if I had the same thing? You have me wondering now because what you are describing is exactly what I'm hearing and I keep saying I think it's exhaust but the shop said nope, exhaust looks good.

 

i bottom out in an uneven gravel lot, a section of the flex pipe was scrapped. you can easily see it when underneth the car.
also, i know some G have full underbody skid plate. but mine was left completely open from the previous owner.

if you expect you have a TINY hole on the flex pipe that you cannot actually see, that will not cause any issue.

this might not be my idle issue either.

stick a camera underneth the car and take some pictures and when the muffler shop has the car up, see if they will let you in to show you.

 

I didn't read this whole thread, but has anyone recommended taking a look at the motor mounts? I bet you one or more are bad causing the vibrations..

 

Canadian, are motor mounts something I as a non-mechanic can see if I open the hood? Probably not but just asking. Also to clarify, the noise I'm getting sounds more like there's a load on the engine, exactly like when the AC compressor is on but in this case it's not on. It seems like when I"m sitting at idle at a red light, I have the AC on or something and I don't.

 

exact same situation and sound for me...

 

Not sure man, sorry . I would imagine any competent mechanic could easily inspect for you.

 

Morningla,
Do you think it could be our motor mounts?

 

2 things:

1) Spark plugs - when they get about 60-70K miles on them they are worn and gaps generally are 10-20mm over spec. If you haven't ever changed spark plugs on your car and you have 60K or more, I would change them.

2) Motor mounts. These can go bad as they are made from a hard rubber. There are not many people that have to replace these BUT if the previous owner drove the car hard it could have put a lot of stress on them causing premature wear. I dont think this is as likely, but it is possible. Not a lot of motor mounts go bad until higher mileage, very few that I have even heard about on these cars. I know people that have 100K miles with a lot of boosted/nitrous/etc miles. No problems with motor mounts.