Hopefully our ford guys can help with this or maybe steer me in the right direction. When adding more timing the idle raises to about 800rpm. Now what that does is also raise the idle so when I let off the gas from cruising speed the idle will drop to about almost 1300rpm and hang there till about 2-3 mph and finally drop down to 800rpm. The idle stop screws are no stopping it from returning as I understand the air idle control completely operates idle. What can I do to make the 1300 rpm be closer to 1000 rpm just before coming to a stop. The car runs so much better with the timing bumped up and i dont want to move the timing back just to adjust the idle. Anyone have any ideas?

 

It's actually doing what it's supposed to do with the VSS hooked up. The idea is that the IAC keeps the idle high enough while the car is moving to prevent bucking.

Your idle may be a little high if you have the actual idle adjustment screw over-adjusted. It has been said that if you have that screw adjusted properly the car should die if you pull the plug off the IAC (in other words, ONLY the ECU should be controling idle).

The computer may also be keeping the IAC open more if the throttle positioning sensor is not properly adjusted. With the key to "run" it should be only sending .9 volts back t the ECU (IIRC). You may want to check that one over at the Mustang Corral though.

High ECU-controled idle can also be a symptom of a bad coolant temp sensor (the one on the heater "manifold"). If that sensor is out of range teh ECU does not know when the car is warmed up and continues to run a high idle and keeps the system out of closed-loop.

As with any suspected problem, run a KOER and KOEO test and report back with the codes that come up. If it's your coolant sensor or throttle positing sensor the computer will most likly tell you. Is the check engine light on?

Good Luck,
-Jason

 

Jason, I am clear on the vss function and I agree it is working as normal. The idle does come down to 800rpm which is very close to (625 to 750) so I am okay with that.It is the high idle when you let off the gas is what is bugging me with holding the idle at about 13oo till it drops. I ran a engine off test and came up with 81 secondary air injection, 82 air bypass, and 85 canister purge. Remember I am not using the air injection portion of the harness. Was not sure on how to run the engine on test. Do you keep the wire grounded and just start the car? Can you refresh me on the engine on process. Also I have no check engine light on either. Tps voltage is at .95 .It appears that between .9 and 1 is going to be okay. One thing that I thought of is that I am running a 65mm throttle body from a lightning. Just wondering if the tps is the same for both. If not then I may be giving the computer wrong voltage... Not sure. Pulled off the air idle control and cleaned. Didnt appear to be that bad. Looked at the one idle set screw and it appear not to be holding the plate open....

 

What I have decided to do is to reset the idle which requires reseting tps if not within specs. Here is the process that I have found to do so. Take a look. I will let you know how it works out.

1.) Get your engine to running temperature.

2.) Un-plug IAC while the engine is running, if it stalls turn idle screw 1 entire rotation, re-start staab throttle, continue this until it idles without the IAC plugged in.

3.) Set the idle to desired level (750-MILD 900-BIG CAM) by adjusting the idle screw, always tap the throttle so it lands in its natural location.

4.) Set TPS between .96 AND .98 Volts with a multi-meter. Loosen the screws and move it around while the meter is attached. Drill out holes more if you can not reach proper adjustment. Use the 2 volt (DC) setting on your multi-meter to get most accurate idle reading. (Do this while the car is still running.)

5.) Stop engine, disconnect negative battery cable wait 20 minutes to reset computer. Turn on headlights and tap the brakes a few times to drain the remaining power. I leave the headlights in the on position the whole time to make sure all power is drained to make sure the computer resets.

6.) Re-Connect the IAC

7.) Re-Connect the negative battery cable.

8.) Start engine, and smile the pain is over! Unless of course you have a bad TPS, IAC, or EGR. LOL.

 

Okay, After following the directions above all my problems were solved. It appears that after resetting the idle it lowered the high drop down (off the gas Idle). I am good to go with about 20 miles of drive time .