Car would not crank over?

This has been ongoing for several weeks now. I thought it was my starter based on Google research, however, I am by no means a car expert or mechanic and fear I might have made the problem worse. I replaced the starter with what I hope is the right one, I had the guy at the shop verify it for me based on having a 1.6L turbo. After I replaced it the only other thing I did was keep the plastic piece on the top of the engine off, as requested by the YouTube video I watched for instructions. I got it to start after replacing the starter but now it sounds a lot more harsh when starting the car, and the same type of problems are occurring from before it stopped starting in the first place. Previously, my tachometer would work intermittently, and my check engine light would come on when it would start working again, and the check engine light would turn off when the tachometer would give up. Also if I sit in idle, at lights or on breaks at work, every now and then the engine will just shut off. It hasn't stalled or anything while driving, only when idling, although sometimes idling for a very little amount of time. I need some guidance on what to do before I give up and take it to a shop and put more money on a credit card instead of fixing it myself, any questions of feedback is welcome so I can save money in this weird time we're living in, thanks all.