1997 Saturn SL1 Error Codes P0300, PO122 & PO340 on 97

So, I have a 97 Saturn SL1. The check engine light came on about a month or so ago & the engine was running really rough with a high idle (2000+ rpms). I used my code reader & got codes P0301 (cylinder 1 misfire) & P0507 (high idle error). I had a mobile mechanic diagnose it as the intake manifold gasket & also said I needed a fuel injector (he said the cylinder 1 spark plug was not getting any fuel). Anyway, the mobile guy flaked on me so I took it into a shop & they fixed the intake manifold as well as replaced the radiator which was leaking. Unfortunately the check engine light is still on & is now throwing totally different codes PO300 (random cylinder misfire), P0122 (throttle position sensor) & P0340 (camshaft position sensor). What could possibly be wrong & why do I have all these new codes coming up? The guy at the shop seemed to think it was my ignition coil. I have replaced the plugs & wires btw. The engine is still running rough (tough to accelerate, not a lot of power) Any assistance is greatly appreciated