1973 450 Air cleaner sensor

[Stanton]

I am restoring the family 450 and need help with the idle. With the old air sensor the engine idle was 2100+. With it disconnected the engine idle is below 500 and barely runs until it stalls. I replaced the air sensor and the idle is 1800. Disconnected it is same as before. Any suggestions for my next step?
Thanks Stan

[Tomguy]

A 1973 4.5 would be D-Jet and the #1 cause of any running issue with these, especially after sitting, is going to be vacuum leaks.

That being said if idle is actually 2100+ RPMs, and it's not "Surging" (slowing down, then racing back up) due to the way D-Jet works, the throttle position switch is either bad, dirty, or not adjusted properly (long story about how it operates, there's a manual you can get if you like).

[Stanton]

Thanks. I'll check it out.