Apparently, with LN, the game generates a new car every time a Sim drives somewhere and they then go into their inventory once all the parking spots are filled. I don't know of any non-mod fixes.
actually i do not have the LN expansion yet, but i do have latest patch for base Sims 3, [1.17], is that mean technically I'm playing the latenight executable?
i thought, LN came out after the 1.17 patch? I'm guessing fastlane is the culprit. but before i read your post (lilygirl), i do,
maybe, found the solution, i changed my active household to the one with so many cars on their inventory, this household has 9 sims, 8 of them are capable of driving, so each of them have a car (which i never buy), some have like 15 "big lemon" cars. what I did is, i sold them off, and leave only 1 car per sims. i bought the parking spot and scatter them all over the house, put each car from each sims to the parking spot, and one by one, each sims, i clicked the car and clicked the "Make preffered car", so every sims has the "preffered car". and now i read your post saying "the parking spots are filled" maybe my guess is right. have you tried this? because so far, i do not see their cars multiplying yet.
and i don't know is this just my feeling or true, but after deleting all that magic cars, my stutter (which many people are suffering) are reduced.
of course that "solution" was just my hunch. but I just want to share.
Thankyou.
(i do apologize if i made any grammar mistake on this post, because I'm not good in past tense)(any critic will be great, since i have to learn english, thankyou)