IS is not pure e53.

For example, all e36 IS cars were two door. The I was a four door.

The first two years of the e70, there was a 3.0si.

And there is a difference in the xdrive cars which I believe started in 2004 on the X5's.

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2001 E53 4.4 Alpine White, Sports Package
2000 E36/7 2.8 5 speed Bright Red w/ a HT!