Installed 52mm BBK, now High Idle

[JayD]

I installed a 52mm BBK TB on my 85 with a manual tranny a few weeks ago. I disconnected and reconnected the battery. Everything was working great with idle about 800 RPM, but slowly the idle speed has crept up, and now it is 1500 RPM. Any ideas about what is causing this slow increase in idle speed

 

[Edmond]

Make sure the cables and such attached to the TB are correct. It shouldn't idle higher because of the new TB. Are there any other mods to the car?

 

[vetteboy86]

I think the throttle cables are a set length. There are no adjustments on them. However I could go with Edmonds suggestion. If that is the only mod you did, whatever you did at that point has caused this idle problem. Is one cable not fastened right. Is the throttle returned to the right position.


Craig

 

[JayD]

The only other mods I have are: K&N, open lid, and cleared MAF.
If anything the cables have a small amount of slack since installing the new TB.
Yesterday I reset the ECM, and the idle was 800 RPM again, but on my way home this evening it was already hovering around 950 RPM.

 

[Edmond]

I still it has something to do with the TB cables because the other mods wouldn't cause a higher idle. I would think the butterflys are a little more open than they used to be and those are controlled by the cables.

 

[rrubel]

Is the throttle able to close properly? I've noticed with my new install that the throttle seems to stick open a small amount after I let off the gas; I'm going to try lubricating the moving parts this weekend.

However, if you don't mind the obvious question, did you make sure the idle was set properly after installing the new throttle body? When I replaced mine, the car wouldn't idle at all. Turns out the idle set screw was too far in. Reset the IAC and adjusted the screw to spec, and it idled great.
[RICHR]

 

[Hib Halverson]

The only other mods I have are: K&N, open lid, and cleared MAF.
If anything the cables have a small amount of slack since installing the new TB.
Yesterday I reset the ECM, and the idle was 800 RPM again, but on my way home this evening it was already hovering around 950 RPM.

Take the aftermarket TB off. With your engine set-up you hardly need it. In fact, a TB that big on a stock or near stock L98 may actually hurt performance, especially response.

But if you insist, you want to make sure of several things 1) continue to try and verify that the throttle cable is not a problem 2) get in touch with the maker and find out if the minimum air adjustment needs to be altered or checked 3) Make sure your IAC is working properly, 4) make sure your TPS is adjusted properly 5) check with the maker and see if a different calibration (chip) is needed to make that TB idle correctly and 6) make sure there are no vacuum leaks and that includes verifying that the TB gasket is sealing properly.

 

[XtremeVette]

I too have heard this.....

Iam gonna have to agree with HIB.

I have done a lot of reading about throttlebody's.....just isn't worth it....especially on a stock or even mildly stocked L-98.

Let me share a little information....were you aware that GM uses a 48mm (our stock TB) on there newest 502 engine? Thats right GM claims that TB is good for up over 500 hp....Now I know who's to agree with GM right? But in addition to them I have read post after post on plenty of different corvette forums....every single one said the same things this is what you can expect:

1. You will only get a small if anything increase in HP. (5 is about it)
2. You will get a little better throttle response though.
3. For the amount of money many people pay to get their 48 trimmed out to 52.
4. Most people who go any bigger then 52 experience problems such as bad idleing, loss of hp, odd throttle response, computer problems and sometimes even codes being thrown.
5. The new throttle body serves mostly as something that just looks better then the stock one. Unless you have modified the engine for better flow and port matched the intake to the new larger diameter TB....your not gonna feel any HP gains at all.....if you think you are...its psychological.
6. Last and most important.....for the money...you are better off with your stock 48 mm....and keeping your extra 300 or more that you are just gonna waste. If you are lucky enough you will hopefully be able to return the larger TB and get your money back.

 

[Edmond]

3. For the amount of money many people pay to get their 48 trimmed out to 52.

Do you know who does that? How much does that cost?

 

[rrubel]

Dave Koldos is the guy who did mine. dkoldos@ameritech.net. IIRC, for $250 (not his cheapest option) I got a 52mm OEM throttle body, new gaskets, new (roller) bearings, a full cleaning inside and out, and he ground out my air foil to match. He would have done my own throttle body, but he happened to have one sitting there as a core so he sent me that one and I sent him my old one as a core. He's fine with just working on yours, though, if you want.

---
$175 52mm bore, new blades, insert with aluminum and reposition egr
port, walnut shell blast
$45 sealed roller bearing throttle shafts
$25 optional GM throttle body R/R gasket set
$8.75 return shipping
$00 install and match bore air foil if one is provided
---

Works like a champ.

 

[plumcrazy]

had the same problem and it was a really quick fix.
i found that the throttle position sensor was hanging
up on the machined surface of the throttle body
took the tps off and trimmed the lever on the sensor
slightly put it back on reset the voltage and all was
fine. hope this helps you out