F355 ITB vacuum leak

It's been a long time since I've had one of those apart. How did you determine it was there? only asking as the needle valves in the adjacent ports tend to be the culprit more often then not. I trying to recall if there actually is a seal of some kind there, I think it's just a bronze bushing.

I know BMW has moved to double sealed needle bearings in their TB's but the buggers are pricey avg $10 a pop sold in lots of 10. so about $100 for tiny little bearings. Given the small clearance heavy grease should work fine under the backing washer.

doesn't really help I know.

 

I will have to check as I have a set off but it seems unlikely it's anything more than a bronze (oilite) bushing as I don't remeber any resistance that would come from an O- Ring

 

I will put this in terms for the understanding of a person who names their location "lions drag strip". =)

First, probably nothing to worry about. You MAY need to recenter that butterfly, but highly unlikely.

Different than carbs:

The throttle plates are not "open" to allow air to bypass for idle. The idle air comes in through 1 or 2 computer controlled idle air valves (typical). The only reason there are throttle plate stops is to prevent hesitation at the teeniest tiniest throttle opening. Even smaller movement than "cracking the throttle". Just enough preload to keep the plates from getting sucked down when the car is idling (high vacuum). This why they need to be set and then reset whilst the engine is ticking over.

The bypass screws are not idle mixture or anything similar. They are just fine tuning a leak, plus or minus from all of the leakage that you already have. For example, on your leaky shaft hole (hehe), the screw will likely be turned in more than the other 7, so that the leakage is equal in all 8. This is what the manometer is for.

Setting the 4 on one bank: these should all crack at once.

Setting the other 4: these should all crack at once.

Setting the banks to each other via the cross shafts: all 8 crack.

The idle air controller (1996-99) or controllerS (1995) will compensate and set idle speed within a minute or two, after every adjustment. (or 5 minutes, depends on what mood it in and how hot the MAF wires are)

The procedure is written up in ONE of the F355 owners manual. I belive it is not in the first one, but IIRC is in the LAST F355 manual, which may even be Spider only, my memory is blurred by working hard today. Whichever it is, it is applicable to your car.

 

Tim
I have eight brand new rubber air box o/rings #14563 they list at $31.46 each not kidding..lol. I would replace them if you have gone this far.I will send you all eight for $100.00
Michael

 

Tim, I would do a search for people who rebuild SU & Stromberg carbs for old Jags, etc. Resealing worn throttle shafts used to be a big business for them.

 

I clicked to say this also. You may want to try Joe Curto in NY. He does a ton of SU carb work, and if he can't help with the throttles, may possibly know someone who can.

 

I agree with Cribbj, find a good carb guy and get it rebushed. It's a vacuum leak, it'll cause problems and contrary to what some other are saying it is a big deal. The adjustment ports are for tuning... not compensating for a problem. I would recommend getting in touch with Pierce Manifolds. Authentic Weber Carbs, Manifolds, Conversion Kits, Accessories and More! If they can't repair it they may be able to point you to someone who does.

 

Resurrecting this thread as it appears I may have a leak at the TB shaft. It's hard to tell though.

Tim, did you bother to get the TBs re-bushed and if so, by whom?

 

Excellent. Thank you