Hotwire

I have had really bad issues trying to keep my LT4 conversion idling at stoplights, sometimes it was fine, just stumble off idle, then pick up and break your neck, other times it would go into a death spiral and cut off. I believe it to be from the overlap of the LT4 Hot cam and the crappy design of my BBK 52mm throttle body.

The stock tbs have a idle bleed hole drilled into the IAC passage, and seal it off to the idle air bleeds under the intake. the pos bbk has no idle bleed hole and vents it to the main intake passage instead of the air bleeds.

I did the mod to the throttle body that you can find on the net and can say, thank you to the people that put that together.

The stock BBK unit makes it so the engine is completely dependant on the idle air controller for idle. If you are running any type of cam and have the idle set low, the ecm will get messed up and go crazy w/ the idle. If you drill the bleed hole like the stock, the iac only has to make small adjustments instead of completely handling the idle. my truck idles so damn smooth even camming at 700 rpm it's awesome.

I feel we need to somehow let the aftermarket know they are screwing up and point them in the right direction.

ff soapbox:

sorry for the novel, just thought that a $300 piece of crap should be of better design / engineering.

NOMAD

Don't tell em. I'll go out of business

I'll have to say, most aftermarket TBs are crappy. Thats the reason I do my own. They idle, they don't stick, they look stock, they are half price........ Only bad thing is, biggest I can make em is 52mm, and I'm totally out of stock on them...lol

I don't know if it's the lackluster QC on the large manufacturers of what, but I sold my BBK the same day I installed it due to sticking blades.

-Shannon

SVT Killer LV

I adjusted my idle screw and iac and it idles fine.. let the pcm learn your cam it will go away...

FWIW I have a BBK 58mm

ninetythreez

I have a BBK 52mm and it runs, responds and idles fine, but then again I don't have a radical cam to go making a bad idle issue. The one negative thing I did notice is the air foil front section on the BBK is rough finished. I like smooth air flow, so out comes the Dremel. You other guys have a rough finish on the airfoil area?

Hotwire

yeah, mine looks like they didn't get enough aluminum in the mold and you can see where the mold comes together parallel/in line w/ the throttle shaft. it's bs, not worth the $. There is also rough finished flashing where they machined / drilled and didn't do clean up on the holes, found a piece of aluminum that was about to fall off into my intake.

one other thing, they put that anti friction coating on the blades, uh, i'm not a scientist or anything, but why put something of that nature on a throttle body that can be wiped away w/ carb cleaner or gasoline?? Dumb asses need to go back to real world school.

Grease

What mod is that? I've never heard about modifying the BBK TB. where can I find that info?

I have a fairly decent sized cam (234/242) and the BBk 58mm TB and I have my idle set as low as I can yet keep the car running, 750rpm. it makes it lope even more. howevewr if I've been driving the car for a while and I push in the clutch or throw it in neutral, the idle goes down to 400rpm for a while.

I guess thats the price we pay for modifying computer controlled cars

Hotwire

http://www.grandsportregistry.com/te...e_body_mod.htm

it worked great on mine, before my stock converter would just about kill the motor when I'd come to a stop, it would load up, then stumble on take off, catch itself and about break your neck. now it's pretty damn smooth. the idle isn't as cammy, but I can lower it some more and probably fix that. Right now I think it's set to 750-725 rpm. and Grease I was having about the same dip you are.

W/ that hole in the throttle body the IAC just tweaks the idle instead of controlling it all the time, so you don't have to wait for it to respond when you push in the clutch, it's nice.

BigJustinZ28

now will this help if your car is idleing high ??? ?

Hotwire

no, check your programming / Idle Air Controller / vacuum leaks.

Do you have your car tuned for the LT4? if so, drop me a line @ , would like to talk to ya.

Hotwire

anyone running into problems similar to mine?

my vacuum is right when I come down off the revs but after idling for a second or two the vacuum will start to disappear, the ints start dropping like crazy, and the idle drops, it continues like this till the map reads about 75 kPA, then it usually hits open loop, straightens out, then starts the cycle again.

I hooked up a vacuum gauge and couldn't really tell any difference when unplugging different vacuum lines and plugging the ports on the intake or putting a unlit propane torch around the ports/injectors/gaskets etc.

My next step is to pull the valve covers and reset the rockers.

Anyone have anything to add? I'm pretty lost and not sure where to go from here. The vacuum gauge was twitching, but it seemed more like the cam loping than a tight valve.

I have datalogs and tunes if anyone is interested and would like to take a look, I'd appreciate any help.

WS Sick

I wish I had seen this mod a few years ago, I had a 93 T/A with the BBK and it idled like crap no matter what was done, finally after a dyno tune and a drive tune the tuner got it close (still hunted a little), later I added a ported stock when and Poof!! the problem dissapeared, this time I went ahead and am having the stock one bored by Nomad on my 97. I also had some fitiment problems on my BBK as well .

BigJustinZ28

Im thinkin about doing the t/b mod cept I have one related question , when the IAC solenoid is at 0 counts is that all the way closed or all the way open ???

S.J.S.

Wow....I thought the BBK was supposed to be good. I got the Holley that a lot of people had problems with but mine works like a charm and it all went in together with my new motor. I wouldn't rule out anything. Try and change out the TB and see what happens. Put the stock one back on.

Fastbird93

Could this little hole also cause the car not to drop back down to idle right away, per se hang at 1500 or something of the like???

Hotwire

no, if it comes down to idle, than that's not the problem, sounds like you either have a leak, or your IAC needs to be cleaned out and oiled. What are the counts on the IAC when it's idling?

programming has the car idling high when cold, and the iac will roll the rpms down to idle once the car gets up to operating temperature.. hell, your temp sender may be bad too, you'll have to put a scanmaster or something on there to check everything out. I'm not saying you have a problem, but if you think you are, nothing beats seeing what the computer is seeing.

I'm going to pull the valve covers this weekend and adjust the rockers to see if that helps. I may put the stock TB back on there to see what happens, can't hurt. I'll watch my map to see if there is any difference at WOT.

As far as the counts go:

http://www.projecttransam.com/projects6.asp

IAC - Idle Air Controller

This data field displays Idle Air Position counts. On fuel injected vehicles, engine idle speed is controlled by the Idle Air Control motor. Commanded by the ECM, the IAC maintains idle speed by varying the size of an air channel that bypasses the engine's throttle plate. By allowing additional air into the intake manifold, the IAC compensates for engine temperature and load variations. The IAC motor retracts and extends in small increments commonly referred to as counts. A count of 255 indicates maximum bypass and full IAC retraction (wide open), whereas a count of 0 indicates no bypass and full IAC extension (fully closed).