No, those are wrong. The so-called "mandative subjunctive" never takes a past-tense inflection of the verb in Modern English. It always takes the bare infinitive. These are both mandative subjunctives, despite the main clause’s verb being in two different tenses:
- This morning the police are insisting that the car be removed. [unreal case]
- Yesterday the police were insisting that the car be removed. [unreal case]
You don’t ever inflect the subordinate clause's verb in a mandative subjunctive. You don’t use was and you don’t use were; you use be. If you don’t use be there, then it is not subjunctive.
That means that these are completely different in meaning:
- It was important that you went. [real case]
- It was important that you go. [unreal case]
Sentence 3 is the real case because it has a verb inflected into its past tense: you actually went.
Sentence 4 is the unreal case because it has the bare infinitive; you may well have gone or you might not have, but that is not the point here. The point is that the importance was being placed not on your actual departure, but on the requirement of your going.
You can rewrite 3 and 4 using an explicit auxiliary to show the two opposing senses more clearly if you wish:
- It was important that did go. [real case]
- It was important that you should go. [unreal case]
Now sentences 3 and 5 mean the same as each other (real case) and sentences 4 and 6 mean the same thing as each other (unreal case).
This is not the way it works in Romance languages like French or Spanish, but it is the way it works in English.