Time For A New Intake Manifold. Recommendations?

[Jap_Muscle]

Hi Guys,

A few minotiry probably knew about a idle issue i have been having over the past few months, so ive finally been able to check my car in for a diagnosis. After a number of weeks looking at every nook and crany of the intake system we believe the issue is actually related to the bearings of the throttle bodies. We have replaced the AAC, TBS and cleaned out most of the intake side but still seems to be idling at 1500rpm. Replacing the throttle bodies has proven a bit to expensive and unreliable to be worthwhile so i thouhgt id take this chance to get a whole new intake system.

What are peoples experiences?

Greddy - still retains the ITBS?

Hypertune - Big $$ but supposely the best money can buy

Nismo - any experience?

ect

Any help much appreciated.

Edited August 31, 2011 by Jap_Muscle

[Piggaz]

Bearings of the throttle bodies... Fair enough.

Did you try and clean the buterflies?

Have you tried the Tomei throttle paste?

[T04GTR]

yes. you need to either back all the throttle stops off or apply throttle paste. i would be re-setting the throttles.

[R31Nismoid]

Ye another vote for incorrect installation of the TB's, such a common problem that leads to high idle.

[Jap_Muscle]

What exactly do you mean by backing all the throttle stops offand resetting the throttles?

Edited August 31, 2011 by Jap_Muscle

[Moodles2]

At the factory they use a black sealant (maybe it starts off a different color and turns black who knows) on the ITB butterfly shafts to stop air being sucked in.

[Jap_Muscle]

At the factory they use a black sealant (maybe it starts off a different color and turns black who knows) on the ITB butterfly shafts to stop air being sucked in.

Yeh i did some googling and it looks like ill need to do what they did in this.

http://www.skylinesaustralia.com/forums/topic/286728-nissan-gtr-high-idle-and-throttle-body-fix/

and get my hands on some of that Tomei Throttle coat

[GTRNUR]

You could also pressure test the entire intake from the intercooler inlet pipe to identify the leak under pressure. Or when the car is idling, spray brake cleaner around the butterfly shaft ends and listen for a change in engine speed. It will be very obvious when you find it.

If you dont find a throttle leak (or gasket leak in that area), move onto either a pressure test, or block off all the hoses that are vacuum related such as brake/clutch boosters, charcoal canister etc until you can stall the engine or get the idle to drop.

[Jap_Muscle]

So ive taken some pictures of the throttle bodies and as you can see they are pretty dirty.We plan to reset the throttles after cleaning the inside of the bore out including the special paste that seals the flaps shut. We will be applying some new Tomei Throttle Coat paste which should fill up any gaps there may be.

However the original concern that we had was that the bearing (picture 3, cant really see as its behind the screw) seems to be letting air into the chamber.

Any thouhgts on all this?

Edited September 1, 2011 by Jap_Muscle

[eightsixboy]

How can u tell if air is getting in through the bearing?

There is prob a seal in there so if you can dismantle have a look. Can always refit and spray lube around it to see if it goes away.

Edited September 1, 2011 by eightsixboy

[kitto]

There is a seal that stops air getting in through the bearing under high boost. These seals can push out. They cant be ordered from nissan though.

You can buy inserts to put in behind them to lock them in though.

Ive seen them on ebay usa.

[kitto]

That didnt make much sense lol. Damn phone!

[GTScotT]

This might sound absolutely ridiculous and outrageous.... But here goes;

How about a second hand set of throttles for a pittence instead of a whopping dollar value on an aftermarket setup?

Crazy I know... But if your certain your throttle setup is the problem, why not have your stab in the dark at a couple of hundred $ instead of a couple of thousand $??

[kitto]

There is a seal that stops air getting in through the bearing under high boost. These seals can push out. They cant be ordered from nissan though.

You can buy inserts to put in behind them to lock them in though.

Ive seen them on ebay usa.

Ok i'm on my computer now, this was meant to mean;

There's a little rubber seal on the shafts that seal off the throttle bodies. Under higher boost conditions, these seals can push out and cause a tiny leak which is noticeable during idle.

There is a company in the US that makes hard plastic/nylon stoppers that fit in behind these seals to hold them in and stop them from popping out.

If your seals are good, from what i can gather, this is a good modification and i'll be doing it to my engine once the rebuild gets under way.

You cannot buy these seals from Nissan. I think someone already mentioned this.

[Jap_Muscle]

after some more googling (thanks guys i wasnt aware of a plastic seal even being available) i found this.

http://www.xs-engineering.com/xsstore/pc/viewPrd.asp?idcategory=14&idproduct=12106#details

looks right?

[Jap_Muscle]

This might sound absolutely ridiculous and outrageous.... But here goes;

How about a second hand set of throttles for a pittence instead of a whopping dollar value on an aftermarket setup?

Crazy I know... But if your certain your throttle setup is the problem, why not have your stab in the dark at a couple of hundred $ instead of a couple of thousand $??

I hear what your saying buddy. Few reasons.

One is trying to source a 2nd hand set which can be a hassle.

Being second hand who really knows how long these things will last.

Buying brand new is almost just as expensive. $1500 for a new set of throttle bodies

Being a 3L build the setup would benefit very much converting to a single 90tb, so why not. Obviously if i can fix the issue, happy days. But the last thing i want is to piss thousands of dollars in labour for trial and error.

[DR 32R]

Get a Hypertune then. One throttle body only. Satisfying to look at. Having one, I've has some tell me it might reduce response. NA or diesel for response any way.

[Jap_Muscle]

Ill give the tbs fix a go and hopefully its all sorted. If not ill be going Hypertune

check back in a few weeks with a update.

[GTRNUR]

Being a 3L build the setup would benefit very much converting to a single 90tb, so why not. Obviously if i can fix the issue, happy days. But the last thing i want is to piss thousands of dollars in labour for trial and error.

Actually thats not quite true.

Engines that benfit from single throttle intakes are the ones that have massive cams and as a result a poor vacuum at idle and at low engine speeds.

My RB315 with stock cams pulls -20mm more vacuum than a stock RB26 at idle with stock cams. More displacement directly increases low speed vacuuum, and as a result makes the engine easier to tune. The other side effect of and engine with a poor vacuum is that your brake and clutch booster doesnt work all that well if you are driving sedately. Because the engine will only pull a good vacuum level on a gear shift from a high rpm.

So if your 3lt is running 272 or larger cams, then yes you will make the engine easier to tune and nicer to drive with a single throttle plenum. If you are running 260 or less cams, then there is no tuning or drivability benefit. Instead, the engine will actually have slightly less throttle response, because there isn't a plenum full of filtered air at atmospheric pressure directly on the other side of the butterflies only a few inches from the intake valves. Granted we are only talking a tiny difference in throttle response, but it is there.

Have you pressure tested the entire intake system yet to identify the leak? I have tested my intake system at over 35psi and the stock throttle shaft seals don't leak. Once its pumped up the only way air can escape is to blow past the piston rings on the cylinders that have open intake valves.

I am pretty sure the xs-engineering seals arent available any more either. I contacted them once a few years ago when I had a shaft seal leak on my R33 GTR. It used to make a whistling noise at idle. I ended up spraying it with some INOX when testing for leaks and the sound went away forever, and so did the leak. I guess the INOX somehow helped the seal seal again, possibly made it expand a little.

[GTRNUR]

One more thing. Is this a built engine that has been apart before? If so its possible that the wrong alignment dowels have been used in the throttle bodies to align the plenum and base plate.

There are two length dowels in the engine that will fit the throttle bodies. Using the slightly longer dowels that belong under the throttle assembly(that the throttle cable connects too) in the throttle bodies will prevent propper compression of the gasket, because they bottom out in the alighment hole. So you get a leak.