So I bought this 03 cavalier with the Ecotec. It starts ok, idles a little low, and will rev up to the cutoff but if I floor it, it dies! No matter where in the RPM range I floor it, it will either try to stall or bog down and load with fuel.

So I had the air box off one day and I manually opened the throttle body while it was running. It felt like I had air coming OUT of the TB. Can this be compression or am I imagining things??
I get a code for a bad MAP sensor reading.
P0108 map sensor voltage to high so I think there isn't enough vacuum or too much pressure. Also codes for misfire (p0300) and evap problem(p0440)....
this engine was neglected. It has 46k on it and I think the oil might have had the same. It's sludged pretty well. I'm in the process of cleaning it out.

Any ideas? Any tests I can do?

There is a process for checking your map sensor voltage. I was getting a high voltage issue with my intake temp sensor, and it was not noticeable, but was just a bad plug on the sensor its self. A bad map sensor could cause other problems, because that is what the ecotec uses in place of a mass air flow. Your catalytic converter could also be clogged, disconnect the manifold at the downpipe, and while it will be loud, see if it will rev up higher. If it will, i would look into that being the issue.