Odd problem.

I have a 63 dart 225 auto all original. I drive the car 5 days a week 60 miles a day. On my monthly fluid check i pulled in the driveway car was running great. Shut it down cleaned and vacuumed the interior added 1/2 quart or oil ant trans fluid and changed a very dirty air filter.
Well it took long enough to cool off so i fire the car up into high idle to warm it up. No problems 50psi of oil pressure,running smooth. Then i tap the gas to bring the idle down. It starts dropping all the way down until it dies. It runs great at 75mph but *** soon as i come to a stop i have to feather the gas. Its confusing me all i did was add oil,trans fluid and changed the air filter and now it wont idle.


SHORT VERSION: Added 1/2 quart of oil and trans fluid and changed the air filter and car runs great but wont idle worth a crap.

Thanks for all your help everyone.