Picked this Camero up from a guy that had it in storage for aprox 4 yrs. Starts poor, takes several cranks, sometimes need to open throttle to get it to fire up. have tried several things. Changed fuel filter, o2 sensor, found a line off egr, replaced air filters, added fuel injector cleaner (couple times), added methal hydrate too, started up like bran new. However, after driving a bit, this goes back to starting poor. testing with code reader, found code saying egr, o2, replaced o2 sensor and replaced vacuum hose on egr. and reset ecm. all good when i reset ecm, done it couple times now, runs fine, then goes back to hard starting after 50/60 miles driving and seems hard on fuel and as it gets poorer. reset ecm, good for a bit, on codes , it says rich fuel condition, egr/ ecm issues. any suggestions?