So, I bought a used 2006 Rav4 limited 4 cyl. with 108k miles on it. It's been an ok car for now. Since I've gotten it, in June, it seems that every 2-3 weeks, the TPMS comes on and sure enough, all 4 tires are between 7-9lbs low. I have no idea why. About 2 weeks ago, I put 2 new tires on the front when I got a flat that couldn't be repaired and will put the other 2 on in about 2 weeks. (Couldn't afford all 4 at the time. ) Even after putting 2 new tires on, all 4 still go 7-9lbs low. So, what the heck is going on? I have never had this happen with any car I've owned. (Just an FYI, when I got the flat and put the spare on, the rim was not identical to the others on the car but that tire was still at 32 regardless. ) It seems to be just the tires I'm using. Any ideas? Thanks!