View Full Version : fast idle

09-12-2007, 06:12 PM
First of all I want to admit that I have very limited knowledge in regards to carbs...
My Mustang with a FRPP 347c.i./450hp crate engine,holley 750 dp mech secondaries and a single plane vic jr. has all of a sudden started idleing much faster. It use to idle around 750-800rpms's.
Now it wants to idle at around 1000-1200rpms.
I am unable to "blip" the throttle and get it to idle down.
It seems to also want to diesel or run on when I turn off the ignition. I imagine this should be expected when you shut the car off when it is idleing at a higher rpm.?
Do I just need to find the idle screw and back it down a 1/4 turn or so until I find the right setting?
Or could I have other issues?

09-12-2007, 07:28 PM
Possible vacuum leak. Start by checking all hose lines and gaskets.

09-13-2007, 04:40 AM
If it was a vaccum leak youd hear a loud suction or whistle sound. If anything your Idle screw might have turned in during acceleration. Check on the throttle arm side (driver) for the screw to adjust the idle.

09-13-2007, 09:01 AM
Hey guys,
Thanks for the replies.
I will check it out this evening.
Hopefully its just a turn of a screw and we are good to go.:fingersx:
I will check for leaks as well why I am at it.

09-17-2007, 05:44 PM
Make sure the choke is opened all the way and the fast idle cam is not engaged.

09-17-2007, 06:24 PM
Turned the idle screw down about 3/4 turn and it went back to normal idle. I'm not sure why it bumped up about 350 rpm's?
Hopefully it will stay at the appropriate level.
Thx for the responses.