No myth, the balancing of the throttle bodies relies on the Bernoulli principle. As the incoming air has to rush past the opening between the closed throttle blade and the bore it has to speed up, this decreases the pressure. This pressure lower than atmospheric is what you register on your water manometer (the other side of your manometer is open to ambient pressure, and the reason you use a water manometer is because it is more accurate than a "Hg one, which wouldn't even register the small pressure drop)
Since your pressure drop is dependant on the actual flow debit, any introduction of "false" air which bypasses your throttle blade will reduce the flow debit past your plate and as an effect it will effect your readings. This is why you plug the IAC. If for instance on TB has more false air than the other, how are you going to balance them properly with your readings? You can't. The adjustment stands and falls by the assumptions that both TBs are equal where it comes to flow debit (and as such the amount of false air)

Now, you are saying a vac leak at the shaft won't give problems. It DOES and if you say it doesn't you have obviously never had a problem with that before. The TB is aluminium, the shaft is steel...give it some miles and the housing will wear out. This gives a vac leak, an additional source of air coming in. This wouldn't be a problem if it were a constant leak and if the leak was similar on both TBs, you could set the minimum air setting lower and the IACs would adjust to a lower position to get the idle rpm down.

However, the leak is not consistent as the shaft is spring loaded and the throttle, TV and Cruise cables on it there's no guarantee the shaft will position itself similarly every time. What matters is if the bulk of the leak (given by a shaft in an oversized bore) is above or below the throttle plate. As the throttle closes it can position that shaft in the bore differently each time. This will give a surging idle or intermittent high idle as the ECU always strives to reposition the IACs to an ideal setting (within a pos # range, usually around 10). When you drive above 35mph the iac pos. is reset, you idle down, when rpm drops the iacs open to pick up the engine before it stumbles and dies, however they go to the ideal position and then the adjusting begins to regulate the idle.

Now, you tell me how that air leak won't affect anything? Find a car with worn tbs and start wiggling the shaft with the engine idling. You can scream BS, MISINFORMATION and whatever, but the idle changing right then and there...what does that prove?

What you are doing here is a simple case of dirty tactics, starting crap on the CFI forum to run off the guys from DCS and now you are sneakingly taking a stab at them because yes, they do offer a rebushing service.

 

I had my TB's re-bushed by DCS and the proof was in the results - the shafts were loose before and are now nice and snug , the difference in idle after as compared with before are a world apart. The guys at DCS really know their stuff and what is worth a whole lot more is that they totally back their products and services. I had some issues with the balancing of my TB's (all due to my inexperience and lack of understanding of the process and nothing to do with the bushing service they did) and the guys at DCS were on the phone to me several times until I was crystal clear with what I was doing and had her running as sweet as can be. That support alone is worth more than the $$ you pay for their products and services .

Integrity is worth a whole lot IMHO

 

I'll third it! Had mine fixed and all the difference in the world on idle and balance. Not sure if it's big impact beyond that but certainly at idle.

 

my rear tb shaft was so worn that at idle it would whisel .found a new rear tb[on e-bay] for less than having a bushing put in .car now runs great[smoother] and does not whisel .

 

thanks for the advice. i purchased a new fuel pump and ran into another problem. the car wont start. on the fuel pump cover, i have a tan wire for the sending unit, a black wire(ground) and a brown wire. i connected the positive of the new pump to the resister and the other pump lead to ground.is this right?

 

Vtwin;

I did not mention DCS. As it happens, I know those guys personally and I like them both. Before they ever started their web site or did their first re-bush job, it was I who located the carb shop in Phoenix (where I lived at the time), spoke to the mechanic about crossfire TBs, got a price and arranged for Tom to take his TBs there for a re-bush. Don't presume you are going to tell me anything about DCS. Tom and Jim and I have disagreed on a lot of things lately, but I do NOT do standard re-bushing jobs, and I DO continue to refer people to them so your implication is completely unwarranted.

I am an engineer, but you don't have to be technically competent to look at the underside of a 4 banger throttle body ad see the relative size of the IAC pasages and the worst possible vac leak you could have thru an additional .002 clearnace on the shafts. Since you have such decisive opinions, I can only assume you have experience in the actual meaured wear on a typical crossfire throttle body shaft.

ANY vac leak past the shafts would be BELOW the throttle plates and nowhere near the balance port . . which does NOT see manifold vacuum incidentally. The TB shafts were never SEALED even from the factory, so you are at best only talking degrees.

Coincidentally, I did Zixxer's TB bushing job with Teflon bushings. His problem went away, but not because I eliminated some perceived vac leak.

The reason that new bushings correct some problems has everything to do with the accuracy of the linkage and NOTHING to do with vac leaks. Actually your discription was fairly close to what actually happens. I would not know if that was accidental.

I contine to find it unfortunate that some people make everything personal rather than sticking to hard facts.

Correcting loose shafts fixes a problen, true enough. If people want to think that was because it eliminated a vac leak, well that's their perogative.

 

You're right Steve, a little self checking may be in order.

WOW!... OMG! First, I can't beleive you said that knowing very well that its the truth about the shafts. If the shafts are worn out and you balance the TBs perfect even, as soon as you move the linkage they are out of balance, true statement. We have proved to a TON of CF owners at our workshop events that it makes a big difference and I'll just let that stand for itself on its own merit.

Second, That's a "VERY" cheap shot Steve. Man... I can't beleive you would do that in open forum, but you did and we all know what you're all about now. You never stop with the digs if you can get them in there no matter what, you know what they say about what goes around, comes around. I'm sure yours is coming.

You can reply to this thread until your blue in the face to justify your comments, but it just doesn't matter anymore to Jim or I what you say. We both know you for what you are now. Hey, could you pull that knife out of my back now? You know you directed that bow shot at us.

 

Tom, you know that it was me who told you guys about the off-idle balance issue and I arranged for you to get your TBs re-bushed at the carb shop in Phoenix.

Just because is seems logical to you that the problem is due to a vacuum leak, and you then tell 'a TON of CF owners', does not make it a fact. And I do not 'know it to be true' as you claim.

We disagree on a lot of issues. You and Jim have taken plenty of shots at me. The difference between us is that I don't whine about it and make it personal.

Take a lesson from Vtwin. At least he explains his reasoning. Any time anyone, not just me, disagrees with you, instead of defending your opinions with facts, you start with the drama.

 

the new pump should come with a new connector, if you bought the 85 vette unit. Turn the key on (car off) listen for the pump to prime. If you hear the pump and still no fuel at the TB the the wires are backwards and the pump is spinning the wrong way.