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Discussion Starter #1
I'm working through a low idle + stalling issue on my '95 5.8L. First I pulled codes and got an EGR code. I discovered my EGR tube was completely severed so I replaced that. Then it wouldn't start. Troubleshot that down to a broken starter relay. Once that was replaced, it started but still idled around 400 rpms and would die. I'll put a new IAC valve on this afternoon, but all of this leads me to my question...

What does the Idle Stop Screw do in relation to the IAC valve? I.e. - if the PCM controls idle speed with the IAC valve, what is the stop screw for?
 

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The Anti Yam!
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It sets a bottom low speed base idle, used as a buffer.

Lower than the computer would want it to ever drop. Think of it as a "Limp Home" mode for the idle in case something goes wrong.

I always set mine slightly higher than spec for a better buffer, but still low enough for the EEC to control idle via the IAC.

This is how I set mine.
Gacknar said:
1. Start engine

2. Warm engine to operating temp.

3. Remove the plug on the IAC.

4. Turn the throttle stop screw until you reach 600rpm.

5. Turn off engine but place key back in on position.

6. Test the TPS. It should read .90, if not adjust it till it does.
http://fordfuelinjection.com/index.php?p=30

7. Restart engine, is idle still at 600? If yes then continue to step 8. If not repeat 1-7 until you have 600rpm idle with a .90 reading on the TPS.

8. Reconnect IAC.

9. Idle should rise to around 640rpm.

10. Have a beer because your idle is now set.
 

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Discussion Starter #3
Ok, thanks. That makes sense to me.

...and just for the record, I did find your idle set procedure via SEARCH. :whiteflag However, the one I found didn't have Step 10, so this one is vastly superior! :beer
 

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There is a Ford Racing Performance Parts "idle setting procedure" Instruction Sheet (Techline (800) FORD788) steps 1-9 on How To adjust idle by disconnecting the IAC using the throttle body idle stop screw, drilling out the mounting screw holes on a newer "plug & play" TPS so you can adjust it for voltage setting.

In the past the ideal setting was thought to be .93-.97 volts or just under 1 volt but recently posted information regarding this appears the setting should be between .55v-.75 volts.

Posted by FSB member Jermil01:

Wanted to update this thread based on some TPS adjustment information I got from one of my tuning sites. This goes against the conventional wisdom of setting the TPS closer to .95 range. Thoughts??

Regarding any ECU controlled function (and idling conditions in particular), before any strategy based adjustment can be made by a computer controlled system, it must first run somewhat normally in a default and OL mode.

To do this with a FORD you must first follow a few rules.

You must keep the TPS input above the deadband area and below the "tip in" area. On a FORD this equates to below approximately 0.9V and above 0.45. Anything above 0.90V the ECU thinks the throttle is starting to open. This brings into affect possible dashpot and fuel cut strategies which can turn one grey real fast. Below approx 0.40-0.45V the system suspects an incorrect input and substitutes a default figure.

So first off, the TPS should be set to around 0.55-0.75V.You can also disconnect the IAC then disconnect the battery for 15-20 minutes, reconnect and the computer should default back to factory settings.


See if that helps!


Good Luck ~ :thumbup
 

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Discussion Starter #5
New IAC valve solved it. I only had to replace a faulty EGR tube and starter relay to get to the IAC. :histerica But the TB & MAF got a cleaning during this process, so it's all stuff that needed to be done.

Next up... replace the exhaust that rusted off!
 
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