Mechanic repairing hard starting removed push rods. The push rods from cylinder number 5 were replaced but the short rod and long rod were put back in the wrong position, Started engine and had knock. Engine ran for a while. Finally determined fault and had head sent to be repaired. Got car back and ran rough while at idle in drive and reverse but was fine in neutral. Engine light came on and then went off and finely after several weeks stayed on. During that time starting immediately after receiving car back I was told by mechanic to use an additive and high octane fuel to clean the injectors, this did nothing. Had car checked and found compression lost in number 3 cylinder. No determination as to whether the damage to #5 could have affected more than just #5. The engine analyzed shoe that #5 was missing constantly. What could the mix up in rods done to cause this?