Yes, there is a difference.
I have meant to do it.
This is the present perfect tense. It looks back at the past and includes the idea of "now".
I have meant to do it. (You still mean to do it now.)
I meant to do it.
This is the past simple tense. It refers to an event in the past that is finished and does not include "now".
I meant to do it. You meant to do it in the past. ( There is no reference to the present time.)
The above is acceptable usage in America and in Britain.
However, there are different rules for the use of the past simple in British and American usage. When you are reading American text or listening to American dialog, you need to be aware of the differences.
In American usage the past simple is often used for recent events when the present perfect is preferred in Britain. The past simple in American usage can be extended all the way up to the present moment, but not including the moment when the speaker is actually speaking. This gives to the past simple almost the same meaning as the present perfect tense when referring to recent events.
I meant to do it. (From a time in the recent past up until now)
I have meant to do it. (From a time in the past up to and including now)
I already ate.
I just arrived home.
I just did it.
I already did it.
I've already eaten.
I have just arrived home.
I have just done it.
I have already done it.