I have a 200 to 400ft error on the altitude display (toggles between 750-950feet) with a baro of 29. Anyone else seen this issue before? My actual altitude is 450 ft.

i have no idea about that, i tend to ignore the data our MMCS gives us sometimes, it says my average speed was like 30 when i been doing like 80 every since i started the car and my mpg some how is like in the high 30s, idk lol

I have noticed this. Since I'm in Denver, of course I know that altitude downtown is 1 mile up (5280ft). I love north of downtown, which is higher in elevation by maybe 100 ft or so, maybe even more. My altitude on the car at my house usually says 5150ft. If I compare it to my Garmin GPS, it's off by 2-300 feet, all the time. It'd be nice to rely on that.

Keep in mind that GPS elevation figures can only be calculated if you are hitting off of 4 or more satellites. Plus, those satellites are 12,500 miles in space. Almost all GPS devices are notoriously bad at calculating elevation. I always thought it was kind of a gimmick anyways -- kinda like the lap time feature.

if it can pin point you on a street in a metroplex maze then it should be able to give you the correct altitude and not change as much as 600ft. If it does take altitude off of the gps then where is it getting the baro indication as that will change your altitude. I think its a crappy sensor used by the ecu.

its swinging from 350 to 950ft now. And the correct altitude is 500ft not 450.

That's untrue. My Garmin shows exact elevations, where the MMCS does not. Saying that GPS is incapable of determining correct elevation, is incorrect. If it can't determine elevation correctly, then that would mean that other calculations that GPS provides (i.e. speed, location, etc) are incorrect. Having a fix on multiple satellites makes that fix more accurate. I can usually pick up between 8 and 9 sats where I am. I see the same satellite fix results from both the MMCS and my garmin. Even pulling out my garmin handheld GPS/FRS radio, it shows near identical results. The MMCS is always off by a couple hundred feet.

Show me proof and studies where GPS is used for elevation calculations, but greatly differs from actual elevation. Even flying a plane, the GPS calculated elevation is near exactly what the oldskool gauge shows. I can understand it being off by a few, even double digit feet (10+) but not several hundred.