I have not heard of that before. You might also check the vacuum system. If you faild to connect parts of the vacuum system, the car may have difficulting adjusting for an idle circumstance. I kno my 90 galant wouldn't start for a bit b/c we removed a line that i suppose was important, and it didn't compensate for it.
Not sure i've ever seen a car with a fixed throttle, that can't be adjusted though, Also, i might mention that these old-car gear heads will and can make any engine swap possible provided it's mounting the same direction. buddy of mine has a 5.3l Silverado engine in a 81 Buick with all kinds of custom adjustments. He gets 30mpg on the highway, which is sorely upsetting.
also i apologize for posting 2 weeks too late. been busy.