Is TPMS standard or an option? I have a 2007 E550 with 4Matic and P2 and I can;t find the settings on the instrument cluster menus. Does this mean I have no TPMS? is this something that I can add?

TPMS was NOT available as an option in US Spec cars in 2007. Canadian cars had a rudimentary system (mandatory by Canadian Law) which ran off the ABS system which would alert the deiver that one of the tires was at a lower pressure than the others.

MB had tons of problems with their TPMS so they decontented it in 07 to better their JD Powers ratings. No crummy TPMS=no complaints. Before 07 it was an option. I had it in my '04. ...and it crapped out frequently.

You are better off without TPMS, in my own opinion. Just another gadget to break. I don't have it in my car, which is fine.

How often do you guys recommend that I check the pressure manually? Is there a specific gauge that you recommend?

Once a month. I use a round dial guage with a brass stem. Buy a good one, keep it in the trunk right rear net compartment. Don't drop it. Be sure tires are cold.

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Its a great thing to have. The more often you check your TPs, the better the handling and the longer the tire life. Its just the pre-'07 MB units broke all the time. Thats over now. They're good.

Do you think it makes sense to have a good quality portable compressor with a tire gauge? This way if you have a slow leak, you can quickly inflate the tire to at least be enough to to a safer area if that's an issue. Any recommendations?

No, actually TPMS is Federally required on all cars sold in USA from 2007 on.

I have two 2007s, but the one actually built in 10/2006 doesn't have TPMS and the one built in 2/2007 does.

We can all thank Ford Explorer/Firestone for this requirement.