The automatic 2004 Mazda RX-8 I looked at today had a rough idle. The guy said it was because of a rotary. Tru

Yes, it is true that rotary engines have rough idle. It is due to the fact that they have low compression. If you are concerned, you can take it to a mechanic to check it out. One thing to remember is to NEVER put synthetic oil in it. It probably needs a tune up.