I have an 05 Touring with 75k miles. With the van running and in park, the rpms are at about 700-800. I noticed while sitting somewhere for an extended period of time that about every 1-2 minutes, the rpms would drop to about 500 and then quickly jump to about 1000, and then drop back to normal. I have never really paid attention to this before or noticed it, so I am not sure if this is normal for the ody. Any ideas?