View Full Version : Accufab Plenum--High idle

12-29-2006, 12:28 AM
This has probably been covered a thousand times,but I couldn't find it when I searched it. My problem is I've got an accufab plenum on my '03 cobra and I'm trying to use the factory throttle body.When I put the plenum on; the car idles at 2900 rpm and when I try to drive it,it wants to rev high also.I've contacted accufab(jerks) they say the only way around it is to use their throttle body. I've got a predator and have tried to adjust the idle using it,but that doesn't work either.Maybe I've inhaled too many fox body exhaust fumes, but I can't believe a less restricted air flow would create such problems.Any and all ideas would be greatly appreciated. Thanks

12-29-2006, 12:07 PM
I believe that has something to do with the IAC throttle bypass port on the stock throttle body which may not align properly with the port that is milled into the accufab plenum. The same thing would happen if you disconnect the IAC connector. I would not doubt that you probably have a pending IAC error code since the RPM is not being controlled by the IAC valve.

12-29-2006, 03:08 PM
The predator doesn't show a code. Could I adjust the IAC somehow?

12-30-2006, 10:39 AM
The only way you could adjust the IAC is to replace the gasket with one that has smaller holes in it for the air passage. I think the issue is the air bypass port does not match that on the wide oval plenum.

I would compare the idle air bypass port on the throttle body and inlet port on the plenum to see if they line up. The wide oval bore throttle bodies have the port milled into the upper section of the plenum where as the stock throttle body has a large hole in the center between the throttle blades. (It has been a while since I took mine off the car so not sure if the stock throttle body has the same type of idle air bypass port that the wide oval throttle body uses and if it is in the same location. If they match it should work.

12-31-2006, 03:47 PM
I decided to remove the throttle body on my 04 Cobra since I have not done so in some time. I took some pictures of the stock intake plenum and the back of the throttle body (in case you no longer have the stock intake plenum).

Since the idle air bypass port on the stock throttle body including the stock intake plenum is larger than what you would find on the Accufab (Billetflow, Kenne bell or Whipple) wide oval intake plenum, the stock throttle body will not work on the aftermarket plenum due to the porting miss-match.

It may be possible to fabricate a throttle body spacer that would correct for the larger idle air bypass port but probably more trouble than it is worth. :(

01-01-2007, 04:47 PM
I fabbed up a gasket out of a piece of plastic. It works, with the right diameter hole drilled in it the car idles at 750rpm. Thanks for all the help. If anyone else has the same problem feel free to email me at stocklx@sbcglobal.net