1986 MGM 5.0.........idle for dummies

[Toploader]

Ok so yes I am a dummy, but I do cop to it!
The car is running too fast at idle, why have no idea just noticed this.
So, I have a tach/dwell that I use for the Studebaker, but I have no idea as to how to check and then reduce the curb idle in my '86 Tudor??
Step by step instructions if you guys can???.........many thanks.
Btw, the trans is shifting beautifully!

[friskyfrankie]

Make sure gas pedal is not stuck under a floor mat (sounds dumb but does happen), accelerator cable sticking, throttle body clean, etc. IAC would be causing stalling issues but if it is not too bad could cause idle issues. Sure I'll think of more stuff later...

[87GrandMarq]

The idle is controlled by the ecu, there’s no way to change it. You might have a sticky iac. While it’s idling pull the iac connector to see if it does anything. It could also be a vacuum leak somewhere.

[friskyfrankie]

+1 On possible vacuum issues in addition to the things I previously listed.

[Toploader]

But how does one actually reduce the curb idle?

[kishy]

But how does one actually reduce the curb idle?

There is a throttle stop screw that sets the minimum amount of open throttle, but you should not mess with this. It was correct at some time in the past and unless you can account for when and why it would have been increased, you should assume that a problem has developed with some other aspect of the engine controls to incorrectly raise the idle.

The idle speed may be high because the computer is intentionally raising it. The computer raises the idle above that baseline set by the idle stop screw to what it believes is correct based on sensor inputs. For example, idle speed is held higher when coolant is cold. This branches out into its own diagnostics tree to figure out what the computer thinks is happening.

The idle speed may be high because of a malfunction in the engine controls, e.g. the coolant temp is thought to be colder than it is, or the IAC is sticking as noted above.

The idle speed may be high because it is being raised by a vacuum leak as noted above. This is the most likely thing to happen if no other changes have happened yet the idle speed is mysteriously higher.

Determining what the idle speed actually is in RPM, and if it is steady, would be useful first steps. A tach can be connected to the ignition coil; I've tried unsuccessfully to find you a diagram showing which terminal, but in most period Fords the terminal you want to probe has 2 green wires going to the same terminal together.

[Toploader]

There is a throttle stop screw that sets the minimum amount of open throttle, but you should not mess with this. It was correct at some time in the past and unless you can account for when and why it would have been increased, you should assume that a problem has developed with some other aspect of the engine controls to incorrectly raise the idle.

The idle speed may be high because the computer is intentionally raising it. The computer raises the idle above that baseline set by the idle stop screw to what it believes is correct based on sensor inputs. For example, idle speed is held higher when coolant is cold. This branches out into its own diagnostics tree to figure out what the computer thinks is happening.

The idle speed may be high because of a malfunction in the engine controls, e.g. the coolant temp is thought to be colder than it is, or the IAC is sticking as noted above.

The idle speed may be high because it is being raised by a vacuum leak as noted above. This is the most likely thing to happen if no other changes have happened yet the idle speed is mysteriously higher.

Determining what the idle speed actually is in RPM, and if it is steady, would be useful first steps. A tach can be connected to the ignition coil; I've tried unsuccessfully to find you a diagram showing which terminal, but in most period Fords the terminal you want to probe has 2 green wires going to the same terminal together.

Ok soon I have to bring the car to my buds shop for a LOF, while there I will have him go over the suspected causes for the idle to mysteriously raise all of a sudden.