Quote:

Here it is...

Right out of the Service Manual:


'The high performance engines (340, 440, 440 3-2V and 426 Hemi) employ idle speeds between 800 and 1000 rpm to obtain acceptable lower emissions during idle and deceleration. In order to prevent "after running", with such high idle speeds, these engines have an electrical solenoid throttle stop which holds the throttle at the correct idle position when energized but de-energizes when the ignition is turned off, allowing the throttle blades to close more completely.'


My little, old '70 340 Duster had it in place...

900 in neutral;it was needed...

Even back when 10.5 compression burned 97 octane...



Nice reference from the service manual.

Because the correct initial timing was compromised to obtain those acceptable emission readings, they had to crutch the system using a solenoid. More initial timing usually drives HC levels up.

People used to hunt only with clubs and sticks, but, we've evolved.

I made a real good living tuning cars in the 80's and on because people wanted to use the factory ignition settings or fall victim to total timing thinking. My 340 with a tight lashed 284/528 mechanical idles nicely at 750-800 rpm, not stinking out the neighborhood with raw fuel, clean plugs and 22* initial timing. It runs like junk with 10* initial and smells like a leaking fuel truck at idle when timed there.

The OP's issue is based in the inadequate initial timing setting.