Apparently I knocked this sensor on the driver side when I replaced the water pump. I need to buy a new one and replace.

Can anyone tell me what it's called ?

Thanks,

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camshaft position sensor

I guess thats why it's been running a bit rough since. Thnx @Nulu

The cam sensor synchronizes the injectors to intake valve opening and, as you have found, gives better idle quality. You will likely have a trouble code stored wit a bad cam sensor.