Hard starts with high idle

Hard to start, starts idles to 3500 gradually drops to about 300 runs rough then stalls. Stalls even quicker if u give it gas I need help! I bought this car under the impression it needed a fuel pump.I put the pump and filter in (brand new), got it running but it wont stay running. It starts after a few tries, jumps to 3500 rpms sounds really good, then u can literally watch the rpms go down in small increments to about 300 to400 rpms runs real ruff then stalls. If u give it gas the rpms do the opposite of what they should they go down instead of up. Ive checked maf, crank, cam, egr sensors, relays all have proper ohms and volts? Compression is about 40 psi under factory specs? Simple Odb2 codes say car needs to b driving more. Big Scanner codes, p1525 p1526 p0443. Which I do not believe are causing the run issue. Ive had mechanic here for hours on in testing everything imaginable.I have the chiltons book too. We are planing on pulling the engine to replace the rings (due to compression test) but I know doing that probably wont fix the main issue. So if I could get some good know how? Anything will help me at this point