This is one of the most frustrating events for a new DIY mechanic. Replacing a part, putting everything back together and still hearing the same thing. I have done this often and for a while I thought it meant I must have done it wrong. But the truth is it is a diagnostic step. Cars are just complex systems and many symptoms have multiple causes, and your first repair may not be the one that corrects the issue. You need to go from “I fixed it wrong” to “I just gathered more information” and each non-working repair helps rule out more possibilities.
First check to make sure the problem is still present. Perhaps the noise is not as loud, or the hesitation not as severe. Try to duplicate the problem under the same conditions it was happening before. Was the engine cold or hot? Were you going fast or slow? Was the AC or defroster on? Take it around the block and see if you notice anything that may have been missed the first time. For instance if it only happens when you press the brake, there is no engine repair that will fix it, no matter how new the part you put in is.
I made the mistake many times of just replacing something else, hoping that would fix it, and it doesn’t take long for that to get expensive and confusing. Instead go back to the first step. Check around where you made the repair for any loose connections or wiring or hoses you may have knocked off when working. It is amazing how easy it is to cause another problem when trying to make a repair. If you are still unsure, get out the camera you used to take pictures before you started the job and compare.
A simple fifteen minutes of calmly going over everything can save hours of frustrated work. With the car shut down go through each thing you did during the repair and just put your fingers on each bolt to make sure it is tightened and look for anything that is out of place. Start the car back up and listen again. It is amazing how much more you can notice when you are not frustrated. If you are still stumped, you may find that stepping away for a day will make it obvious when you come back to it because you are no longer locked into thinking a certain way.
This is where experience comes in. You will make these mistakes a few times, but they will eventually teach you how to think this way and your goal will change from trying to fix it as fast as you can to correctly diagnosing the problem, and you will no longer think of yourself as failing when it doesn’t work out right, but instead know how to continue on.