Compression of 125 across all 4 cylinders will be okay.

Surely if its been running so bad its going to have logged some fault codes? Have you had those read. Just cause the engine management light hasnt lit up doesn't mean theres no codes, never know the bulb might be 'missing'

I'd be checking that pump that was supposedly fitted and if the filter is new check its the right way around! Seen lazy twats cut holes in the floor under the rear seat to do the pumps so see if thats been done gives you easy access

Give it a whirl with the air mass unplugged too, could be faulty and throwing fucked up readings in.