While rebuilding the TPI 350 for my firebird project, I found out that the throttle body was toast, so I ordered a new one from Summit. I decided to go with a big throttle body even though I wasn't putting a cam in, or doing anything fancy with the plenum. I figured it wouldn't hurt, and I wouldn't have to upgrade later if I go crazy and decide to stroke it. So I get Holley's big dual 58mm TB, and put it on.

So here's my problem. When the engine is off, the throttle body rotates great. It doesn't stick, and the pedal feels good. However, when the car is running, the pedal sticks in idle, and you have to hit the gas pretty hard to get the pedal to depress. Of course, this leads to a huge lurch every time I take off from a light, making the car VERY scary in the rain.

Furthermore, once the TB is out of idle, it doesn't like closing up all the way. I'll come to a light, and still be idling over 1k. I have to tap the gas pedal and let it run back down before it'll idle correctly again. This has affected the braking power of the car slightly, and it's just irritating to deal with.

I've been reading the stickies, and I see that it was probably a bad idea to have gone with the 58mm throttle body, but has anyone seen these symptoms that knows if it can be corrected?

For reference, I'm running aftermarket exhaust from the heads back, and a chip.

 

Sounds like a bad TB or a vacuum leak to me.
Check the upper and lower plates, make sure the screws are tight and they arent leaking. If thats not it, send it back defective. I had the same issue with a BBK and I sent it back and they fixed it and its fine now.

 

I have that issue with the stocker on my formula. It only happens in the winter for me. I figure it's my throttle cable.

 

I've been troubleshooting a bunch of vacuum leaks. I'm pretty sure they're all gone though. The only thing left is to just replace any hoses that haven't already been replaced, which might not be a bad idea. Some of them are probably only 20 years old.

Thanks for the advice. If it's still giving me problems, I'll send it back to Summit and get another one. It makes me feel better to know that this isn't a problem inherent in puttung that big of a TB on a stock motor. I was feeling pretty silly.