Idle hunting, Where do I start? Options

[steuspeed]

I'm working on fixing my idle search. All new vacuum lines, plugs and wires. Car starts and runs smooth for about 1-2minutes, then the idle dumps and starts hunting up and down. My ECU knob was turned full clockwise by the PO. I turned it back to the factory setting.

Stock 2.0L 1973 car with Pertronix. Where should I look next?

[saigon71]

Agreed that you are running lean at idle.

Start by turning the idle mixture knob on your ECU clockwise all the way - this is full rich. If this smooths out your idle, turn the knob counterclockwise a click at a time until the engine idle starts to hunt, then back off one click. Give the engine a little time to adjust between each adjustment.

If that doesn't work:

The 1973 model year used a ballast resistor of 270 ohms from the factory - it seems you are missing this. Pick up a resistor of this value and wire it in series with the CHT temp sender. This resistor effectively richens the mixture accross all operating conditions.

Keep us posted on what you find. Good luck!

[JamesM]

Agreed that you are running lean at idle.

Start by turning the idle mixture knob on your ECU clockwise all the way - this is full rich. If this smooths out your idle, turn the knob counterclockwise a click at a time until the engine idle starts to hunt, then back off one click. Give the engine a little time to adjust between each adjustment.

If that doesn't work:

The 1973 model year used a ballast resistor of 270 ohms from the factory - it seems you are missing this. Pick up a resistor of this value and wire it in series with the CHT temp sender. This resistor effectively richens the mixture accross all operating conditions.

Keep us posted on what you find. Good luck!

That^^

Also should add though that the resistor was only used on some of the 73 cars, this (and a few other things) changed through the 73 production run and the later 73 cars use the same setup as the 74 cars. Need to verify your ECU and MPS part numbers to see what is in there. If you search you may be able to find the cutover date/vin as i know that information is out there, just dont recall off the top of my head, and it isnt reliable anyways as a lot of cars have swapped parts at this point.

But, if it is running fine everywhere else, start with the idle mixture knob on the ECU as stated.

[rjames]

Agreed that you are running lean at idle.

Start by turning the idle mixture knob on your ECU clockwise all the way - this is full rich. If this smooths out your idle, turn the knob counterclockwise a click at a time until the engine idle starts to hunt, then back off one click. Give the engine a little time to adjust between each adjustment.

If that doesn't work:

The 1973 model year used a ballast resistor of 270 ohms from the factory - it seems you are missing this. Pick up a resistor of this value and wire it in series with the CHT temp sender. This resistor effectively richens the mixture accross all operating conditions.

Keep us posted on what you find. Good luck!

That^^

Also should add though that the resistor was only used on some of the 73 cars, this (and a few other things) changed through the 73 production run and the later 73 cars use the same setup as the 74 cars. Need to verify your ECU and MPS part numbers to see what is in there. If you search you may be able to find the cutover date/vin as i know that information is out there, just dont recall off the top of my head, and it isnt reliable anyways as a lot of cars have swapped parts at this point.

But, if it is running fine everywhere else, start with the idle mixture knob on the ECU as stated.

Agree. Go slow with the adjustment knob. Each click or two should make a noticeable difference.