Bad knocking at idle

06 tacoma runs good sounds good . When I put in reverse or drive makes loud knocking sound like a rod knocking but doesn't do it all the time but most of the time . Doesnt do it when driving . Sound comes from engine . After about 4 months of this chk engine lite came on . Code was #4 cylinder missfire changed plugs and coil and reset code . In a few days lite came back on said same thing . Swapped coil and plug with another cylinder reset code . Few days later same code #4 missfire installed new injector same problem ..... could it be a knock sensore.... just started having a miss when first acceleratin..but doesn't miss when hard acceleration