High Idle

Car2n

Registered User
I have my car at an SCT tuners shop and they are having trouble getting it to idle properly.
This is a 97 Mustang that has a "Supercoupe" motor now in it. The set up is completely new and has never been ran until now.
It's a 4.3 stroker with the complete Magnum Powers line up. That would include the 85mm throttle body. There are no vacume leaks. (there was one but is now fixed). The car was run using an original IAC and idled high. We replaced it with a brand new IAC and still idles high. The TPS voltage is right where it should be.
Any suggestions?


.
 
Suggestion: unplug the IAC and see where it idles. If it's still too high, then that rules out the IAC as a factor.

It sounds like it's just got too much air getting through. It could be a vacuum leak, but I see that you checked for that stuff already.

I have heard that the MP throttle bodies have two adjustment screws. One adjusts the stop for the throttle blade, and one is for a secondary bypass. My guess is that one or both of those is set improperly.

Also, I read on this board that the EEC takes a baseline reading of TPS voltage every time the car is turned on. So what that means is that the EEC can adjust for some variations in TPS voltage at idle. So, if I had to choose between getting the TPS voltage spot-on and getting the idle airflow right, I would choose airflow. If need be, you may be able to notch out the holes in the TPS to allow for some adjustment of the TPS voltage independent of the stop screw.

Hope this helps somewhat.
 
I'd like them to fool with the screw but they seem reluctant and keep telling me it's fine as is. They also say that the throttle plate is fine.
They are a busy shop and keep jumping from car to car so the're not working steady on mine. He wants to check the IAC wiring but it only has the 2 wires and it was pretty straight forward which was which. I'm confident with the wiring. It almost seems as though there's a vacume leak but they were looking for leaks and did fix one so I'm sure that they have rechecked and they said the leaks were gone.
The car is running good but the high idle is keeping it in the shop and away from some real dyno tuning.
I don't know what is happening when they disconnect the IAC cause I didn't ask.
 
Paul,
First I would look at the adjustment screw I know for the BBK it says to turn it all the way down and then with the car running turn it up till it runs at a normal idle. This is for the idle air control.
The other thing to look at is the TPS if the voltage is off some it can bring the idle up I have had this problem on my car befor.
 
I just got the below from the tweecer forum, and might be helpful. Chris


*******************************************************
Idle on our cars (CBAZA) is always fun. EVERYONE has problems with it at
first. Reading is the key to understanding it.:
Essentially, the computer is expecting a SPECIFIC amount of air at idle.
You are getting more, so it's trying to adjust things to make it flow
that amount of air at idle. Since it can't, it "hunts".
You need to put in the new numbers....

http://eectuning.org/forums/viewtopic.php?t=5758

http://eectuning.org/forums/viewtopic.php?t=5382

http://forums.stangnet.com/showthread.php?t=579887
(go down to my post (A50SN95) and read that one....)

And here are my numbers, but probably to big for you (I have a 75mm TB):

http://elkgrovemustang.com/index.php?option=com_smf&Itemid=26&topic=24.msg27#msg27

Maybe these will help.
Dennis
 
Back
Top