Weird Hissing After Cleaning Throttle Body

[Pwnin O'Brien]

So last weekend I thoroughly cleaned by throttle body as it was pretty dirty and hadn't been cleaned in a really long time (since I owned the car). After I finished cleaning it I put it back on the car and reset the ECU and then did a pedal relearn, a throttle position relearn, and an idle air volume relearn. The car runs beautifully and idles exactly at 750rpm's.

I immediately noticed, however, when I am accelerating above 1500rpm's, I can hear (with the windows down) a loud hissing sound which gets louder the more I accelerate. The hissing sounds like a turbo spooling up.

I checked to make sure that there are no pinched hoses from the intake and everything was reinstalled perfectly. I have a K&N cold air kit on the car. I just thought this noise was normal and didn't really think too much about it, but I now worry a bit that something may be choking. Has anybody else experienced this? Does anybody have any suggestions as to what could be making this sound?

I have another un-related question for anybody who has the K&N cold air kit installed. On the bottom of the intake tube around the filter end there are two hose outlet grommets. I only have one hose physically connected because I didn't have another to hook up. Is there supposed to be two hoses hooked up to it? What is the second (larger) hose for? Is this a hose used on other R50 models? I currently have the larger grommet plugged up.

Here's a couple of pics of what I'm talking about from the installation guide:







Thanks!
Modified by Pwnin O'Brien at 12:42 PM 7/4/2009

[Ron Burgundy]

I've cleaned my throttle body before and didn't experience this.

The only thing that comes to my mind, is a loose connection (especially if you removed the throttle body) and air is hissing out (like whistleing)

PS - How do you like the intake? I've been debating this... is it worth it?

[Pwnin O'Brien]

Hmmm, I thought maybe it was because I didn't replace the gasket between the throttle body and the plenum, but it looked like it was good condition, I just cleaned it off and put it back on. I'll have to do a more comprehensive sound check around the engine.

I love the intake, I don't really notice the horsepower gain (something like 14.4hp in the 5000rpm range) but it makes my truck sound awesome. During acceleration it sounds really good.

[Ron Burgundy]

That's enough for me!

I googled the issue, and came up with nothing.

Did you completely disassemble the tb?Maybe just for good measure, take it off again and double check your work.

I'll keep looking into it and let you know if I find anything.

[Pwnin O'Brien]

Ok, so I have done some reading and I found out that the gasket should be replaced, even if it looks fine. If the gasket gets even the smallest crack it will cause a whistling sound from the throttle body.

I'll replace the gasket and post my findings.

[Pwnin O'Brien]

Well I replaced the gasket as well as a thorough cleaning around the mating surfaces with a brass bristle brush and the hissing has disappeared!

P.S. I also e-mailed K&N Tech support to find out about that hose and they haven't gotten back to me but I'll post their response when they do.

[Ron Burgundy]

Awesome! Good to hear.

Let me know what K&N has to say.

[Pwnin O'Brien]

Well K&N told me that there should be a hose which runs under the engine cover. I did some research and found that only the 2001 and 2002 models have this hose, and the 2003 and 2004 models do not. K&N did not know that Nissan stopped using this hose so they inadvertently put a hose fitting on the intake tube. I have talked to the Engineering department and they are looking into this.

Thanks for your help!!!

[Pwnin O'Brien]

I need help!!!

So the hissing that I originally thought had disappeared had not actually disappeared. I have had the hissing noise for the past 8mos. or so, I just ignored it. I recently had to remove the intake and throttle body to do the throttle body bypass and I figured this would be a great time to get rid of the hissing for good. My solution was to use some RTV gasket maker instead of the gasket from the dealer. The gasket maker went on well and there were no visible gaps. Once I put everything back together and revved up the engine to test for the leak I couldn't hear any hissing anymore, so I figured I fixed the issue.

Well, when I started to drive the vehicle I noticed a new sound. There is a louder whistle coming from under the hood, but this whistling is different from the last one. The last whistle would get louder as the RPM's increased, sounding like a vacuum leak. This new whistle is not dependent on RPM's, it is dependent on the accelerator pedal position when the engine is under load (the issue does not happen with the vehicle in neutral). When I hold the pedal in a certain position the pitch of the whistle will change, as I push the pedal a little closer to the floor the whistling gets deeper and then goes away as I push the pedal further. The whistling sound only happens when the pedal is at this specific position. There's a very small amount of pedal travel in where it will make this whistling sound. The whistle is so loud it can be heard very easily in the cabin with the windows up.

At first I thought maybe the throttle body cleaner I used to clean the throttle body before re-installing it may have somehow fouled up the electronics in the throttle body. I don't have any DTC's but I doubt I have driven the car enough to register one yet. Also, I listened to the throttle body during the power-down cycling (when you turn the vehicle to OFF the throttle body will cycle completely). I heard not strange noises when it cycled so I am assuming it isn't the throttle body electrical motor.

I thought maybe it could be a different vacuum leak but what vacuum changes with the accelerator pedal position? I could see it changing with the engine RPM's but not with the pedal position.

I really have no idea what this noise is and I could really use some help with this one. If anybody has any ideas please let me know, I'm up for anything!

[fueler]

all short ram intakes ive ever dealt with make some sort of hissing sound. and you should be able to manipulate with the position of the butterfly in the throttle body (that means it should change with pedal position -- not RPMs)

its the sound of the air hitting the butterfly.

mine makes it very quietly (cant hear from the cabin) but ive heard cars that have it very loud. Thats why stock intakes have a (restricting) airbox before the filter - to muffle the loud sounds from the intake (at the cost of losing power)

[Pwnin O'Brien]

This new sound just sounds so weird compared to the old whistling. The old whistle made it sound like I had a turbocharger and was audible at all RPM's above 1500RPM's. The new whistle is just a short but loud whistle with a weird tone. IDK, I could just be crazy.

[nbf6165]

Be careful when your messing with that throttle body, especially the butterfly plate. I ruined mine by pulling it and cleaning it. I'm coming from a Wrangler where I would pull that engine apart monthly. Thought I could do the same with the Pathfinder. Apparently the Paths throttle body is "electronic". Screwed it up and had to buy a new(used) one. And dem boys AIN'T cheap.

[Pwnin O'Brien]

Be careful when your messing with that throttle body, especially the butterfly plate. I ruined mine by pulling it and cleaning it. I'm coming from a Wrangler where I would pull that engine apart monthly. Thought I could do the same with the Pathfinder. Apparently the Paths throttle body is "electronic". Screwed it up and had to buy a new(used) one. And dem boys AIN'T cheap.

See, I heard that a lot with the R51 Pathfinders but I haven't heard of anyone having problems with the R50 throttle body. When you put it back on, what were the symptoms of failure? Did you get the SES light or was the TB making any strange noises or did it just stop working completely?

[nbf6165]

I had a very high idle. Went to dealer to get it reprogramed. They tried several times and couldn't get it right. It did throw a code but I can't remember what it was exactly (high idle something). Apparently I screwed up the butterfly. I don't remember a hiss noise though. I do remember having to pay almost $300 for a used TB however.

[Pwnin O'Brien]

Ugh, that sucks. My idle hasn't changed so I should be good, fingers crossed.

[bmlawless]

FWIW - I have the K&N FIPK cold-air intake on my one-ton pickup with a 7.4L and the hiss is incredibly loud. It is very noticeable any time you hit the gas. Like you, I didn't notice any performance difference, but it does sound wicked awesome.